Dual-mechanism thickening agents for hydraulic fracturing fluids

ABSTRACT

The present invention relates to multi-arm star macromolecules which are used as thickening agents or rheology modifiers, including use in hydraulic fracturing fluid compositions. In one aspect of the invention, a star macromolecule is capable of thickening via a dual mechanism comprising (1) self-assembly of the hydrophobic polymerized segments of the star macromolecules via hydrophobic interactions or associations, and (2) association, reaction, or combination of the hydroxyl-containing polymerized segments of one or more of the star macromolecules.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/697,179, filed Sep. 6, 2017, entitledDUAL-MECHANISM THICKENING AGENTS FOR HYDRAULIC FRACTURING FLUIDS, whichis a continuation of U.S. patent application Ser. No. 14/424,852, filedFeb. 27, 2015, entitled DUAL-MECHANISM THICKENING AGENTS FOR HYDRAULICFRACTURING FLUIDS, now issued as U.S. Pat. No. 9,783,628, which is anational stage filing under 35 U.S.C. § 371 of International PatentApplication Serial No. PCT/US2013/057685, filed Aug. 30, 2013, entitledDUAL-MECHANISM THICKENING AGENTS FOR HYDRAULIC FRACTURING FLUIDS, whichfurther claims the priority benefit of U.S. Provisional PatentApplication Ser. No. 61/695,103, filed on Aug. 30, 2012. Each of theforegoing applications is incorporated herein by reference in theirrespective entireties. This application is further related to U.S.Provisional Patent Application Ser. No. 61/760,210, filed on Feb. 4,2013, which is incorporated herein by reference in its entirety. Thisapplication is further related to U.S. patent application Ser. No.12/926,143, filed on Oct. 27, 2010, now U.S. Pat. No. 8,173,750, whichis a continuation-in-part of U.S. patent application Ser. No.12/799,411, filed on Apr. 23, 2010, which claims the priority benefit ofU.S. Provisional Patent Application Ser. No. 61/214,397, filed on Apr.23, 2009, each of which is incorporated herein by reference in theirrespective entireties.

FIELD OF THE INVENTION

The present invention relates to multi-arm star macromolecules which areused as thickening agents or rheology modifiers, including use inhydraulic fracturing fluid compositions.

SUMMARY OF THE INVENTION

A hydraulic fracture is formed by pumping fracturing fluid into awellbore hole at a rate sufficient to increase pressure downhole toexceed that of the fracture gradient (pressure gradient) of the rock.The fracture gradient is often defined as the pressure increase per unitof the depth due to its density and it is usually measured in pounds persquare inch per foot (lb/ft²). This fracturing process (sometimesreferred to as “frac'ing”) can result in the rock cracking, which canthen allow more fracture fluid to continue further into the rock,thereby extending the crack still further, and so on. Fracturingoperators typically try to maintain the “fracture width”, or slow itsdecline, following this treatment by introducing into the injected fluida proppant—a material such as grains of sand, ceramic, or otherparticulates, that prevent the fractures from closing when the injectionis stopped and the pressure of the fluid is reduced. Consideration ofboth proppant strength and prevention of proppant failure tend to becomemore important when conducting fracturings at greater depths where thepressures and stresses on the fractures are higher. The propped fractureis typically permeable enough to allow the flow of formation fluids(e.g., gas, oil, salt water, fresh water and fluids introduced to theformation during completion of the well during fracturing) into thewell.

The location of one or more fractures along the length of the wellborehole is strictly controlled by various methods that create or seal offholes in the side of the wellbore hole. Typically, hydraulic fracturingis performed in cased wellbores and the zones to be fractured areaccessed by perforating the casing at those locations.

Hydraulic-fracturing equipment that can be used in oil and natural gasfields usually consists of a slurry blender, one or more high-pressure,high-volume fracturing pumps (typically powerful triplex or quintuplexpumps) and a monitoring unit. Associated equipment can includefracturing tanks, one or more units for storage and handling ofproppant, high-pressure treating iron, a chemical additive unit (used toaccurately monitor chemical addition), low-pressure flexible hoses, andmany gauges and meters for flow rate, fluid density, and treatingpressure. Typically, fracturing equipment can operate over a range ofpressures and injection rates, and can reach up to 100 megapascals(15,000 psi) and 265 litres per second (9.4 cu ft/s) (100 barrels perminute).

Fracturing fluids: A proppant is a material that will keep a inducedhydraulic fracture open, during or following a fracturing treatment,while the hydraulic fracturing fluid itself can vary in compositiondepending on the type of fracturing used, and the hydraulic fracturingfluid can be gel-based, foam-based, or slickwater-based. In addition,there may be unconventional hydraulic fracturing fluids. Propertycharacteristics or factors that may be considered in selecting afracturing fluid, or combinations thereof, can include the viscosity ofthe fluid, where more viscous fluids can carry more concentratedproppant; the energy or pressure demands necessary to maintain a certainflux pump rate (flow velocity) that will conduct the proppantappropriately; pH; and various rheological factors, among others. Inaddition, hydraulic fracturing fluids may be used in a wide range ofsituations, such as in low-volume well stimulation of high-permeabilitysandstone wells (20 k to 80 k gallons per well) to high-volumeoperations such as shale gas and tight gas that use millions of gallonsof water per well.

The two main purposes of fracturing fluid are to extend fractures and tocarry proppant into the formation, the latter having the further purposeof the proppant staying there without damaging the formation orproduction of the well. Two methods of transporting the proppant in thefracturing fluid are used—high-rate methods and high-viscosity methods.High-viscosity fracturing methods tend to cause large dominantfractures, while high-rate (slickwater) fracturing methods cause small,spread-out, micro-fractures.

The fracturing fluid injected into the rock is typically in the form ofa slurry of water containing proppants and chemical additives.Additionally, gels, foams, and compressed gases, including nitrogen,carbon dioxide and air can be injected. Typically, of the fracturingfluid, over 98-99.5% is water and sand with the chemicals accounting toabout 0.5%.

Hydraulic fracturing may use between 1.2 and 3.5 million US gallons (4.5and 13 Ml) of fluid per well, with large projects using up to 5 millionUS gallons (19 Ml). Additional fluid is used when wells are refractured;this may be done several times. Water is by far the largest component ofhydraulic fracturing fluids. The initial drilling operation itself mayconsume from 6,000 to 600,000 US gallons (23,000 to 2,300,000 l; 5,000to 500,000 imp gal) of hydraulic fracturing fluids.

Initially it is common to pump some amount (normally 6000 gallons orless) of HCl (usually 28%-5%), or acetic acid (usually 45%-5%), to cleanthe perforations or break down the near wellbore and ultimately reducepressure seen on the surface. Then the proppant is started and steppedup in concentration.

Proppants

Types of proppant include silica sand, resin-coated sand, and man-madeceramics. These vary depending on the type of permeability or grainstrength needed. The most commonly used proppant is silica sand, thoughproppants of uniform size and shape, such as a ceramic proppant, isbelieved to be more effective. Due to a higher porosity within thefracture, a greater amount of oil and natural gas is liberated.

The friction reducer is usually a polymer, the purpose of which is toreduce pressure loss due to friction, thus allowing the pumps to pump ata higher rate without having greater pressure on the surface. Theprocess does not work well at high concentrations of proppant thus morewater is required to carry the same amount of proppant. For slickwaterit is common to include sweeps or a reduction in the proppantconcentration temporarily to ensure the well is not overwhelmed withproppant causing a screen-off.

Gelling Chemicals

A variety of chemicals that can be used to increase the viscosity of thefracturing fluid. With any viscosity increase, some type of gellingchemical must be used first. Viscosity is used to carry proppant intothe formation, but when a well is being flowed back or produced, it isundesirable to have the fluid pull the proppant out of the formation.For this reason, a chemical known as a breaker is almost always pumpedwith all gel or crosslinked fluids to reduce the viscosity. Thischemical is usually an oxidizer or an enzyme. The oxidizer reacts withthe gel to break it down, reducing the fluid's viscosity and ensuringthat no proppant is pulled from the formation. An enzyme acts as acatalyst for the breaking down of the gel. Sometimes pH modifiers areused to break down the crosslink at the end of a hydraulic fracture job,since many require a pH buffer system to stay viscous.

The rate of viscosity increase for several gelling agents ispH-dependent, so that occasionally pH modifiers must be added to ensureviscosity of the gel. Typical fluid types include: (1) Conventionallinear gels—These gels are cellulose derivatives (carboxymethylcellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose,hydroxypropyl cellulose, methyl hydroxyl ethyl cellulose), guar or itsderivatives (hydroxypropyl guar, carboxymethyl hydroxypropyl guar)based, with other chemicals providing the necessary chemistry for thedesired results; (2) Borate-crosslinked fluids—These are guar-basedfluids cross-linked with boron ions (from aqueous borax/boric acidsolution). These gels have higher viscosity at pH 9 onwards and are usedto carry proppants. After the fracturing job the pH is reduced to 3-4 sothat the cross-links are broken and the gel is less viscous and can bepumped out. Organometallic-crosslinked fluids zirconium, chromium,antimony, titanium salts are known to crosslink the guar based gels. Thecrosslinking mechanism is not reversible. So once the proppant is pumpeddown along with the cross-linked gel, the fracturing part is done. Thegels are broken down with appropriate breakers; (3) Aluminiumphosphate-ester oil gels—Aluminium phosphate and ester oils are slurriedto form cross-linked gel. These are one of the first known gellingsystems. They are very limited in use currently, because of formationdamage and difficulty in cleanup.

Other chemical additives may be applied to tailor the injected materialto the specific geological situation, protect the well, and improve itsoperation, varying slightly based on the type of well. The compositionof injected fluid is sometimes changed as the fracturing job proceeds.Often, acid is initially used to scour the perforations and clean up thenear-wellbore area. Afterward, high-pressure fracture fluid is injectedinto the wellbore, with the pressure above the fracture gradient of therock. This fracture fluid contains water-soluble gelling agents (such asguar gum) which increase viscosity and efficiently deliver the proppantinto the formation. As the fracturing process proceeds, viscosityreducing agents such as oxidizers and enzyme breakers are sometimes thenadded to the fracturing fluid to deactivate the gelling agents andencourage flowback. At the end of the job the well is commonly flushedwith water (sometimes blended with a friction reducing chemical) underpressure. Injected fluid is to some degree recovered and is managed byseveral methods, such as underground injection control, treatment anddischarge, recycling, or temporary storage in pits or containers whilenew technology is being continually being developed and improved tobetter handle wastewater and improve reusability. Over the life of atypical gas well, up to 100,000 US gallons (380,000 l; 83,000 imp gal)of chemical additives may be used.

In view of this complex requirement profile, it is clear why, eventoday, there is still a demand for new thickeners in the hydraulicfracturing fluids field.

Accordingly, in one aspect the invention provides a polymer compositioncomprising star macromolecules, each star macromolecule having a coreand may have five or more arms, wherein the number of arms within a starmacromolecule varies across the composition of star molecules; and thearms on a star are covalently attached to the core of the star; each armcomprises one or more (co)polymer segments; and at least one arm and/orat least one segment exhibits a different solubility from at least oneother arm or one other segment, respectively, in a reference liquid ofinterest.

The use of the polymer composition in hydraulic fracturing fluids isalso provided.

In one aspect of the invention, there is a star macromolecule polymercomposition comprising one or more star macromolecules prepared by animproved, efficient arm-first living-controlled radical polymerizationmethod, wherein the one or more star macromolecules are represented byFormula (I):

wherein:

-   -   Core represents a crosslinked polymeric segment;    -   P1 represents a hydrophobic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophobic monomers;    -   P2 represents a hydrophilic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophilic monomers;    -   P3 represents a hydrophilic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophilic monomers;    -   P4 represents a hydroxyl-containing segment (homopolymeric or        copolymeric) comprised of repeat units of monomeric residues,        where at least one of the monomeric residues or a plurality of        the monomeric residues is a hydroxyl-containing monomeric        residue, of polymerized monomers;    -   P5 represents a hydrophilic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophilic monomers;    -   q1 represents the number of repeat units in P1 and has a value        between 1 and 50;    -   q2 represents the number of repeat units in P2 and has a value        between 30 and 2000;    -   q3 represents the number of repeat units in P3 and has a value        between 30 and 2000;    -   q4 represents the number of repeat units in P4 and has a value        between 1 and 50;    -   q5 represents the number of repeat units in P5 and has a value        between 30 and 2000;    -   r represents the number of polymeric arms covalently attached to        the Core;    -   s represents the number of hydroxyl-containing arms covalently        attached to the Core; and    -   t represents the number of hydrophobic-containing copolymeric        arms covalently attached to the Core; and        wherein:    -   i) the molar ratio of r to s is in the range of between 40:1 and        1:40; and    -   ii) when t is at least 1:        -   a) the molar ratio of r to t is in the range of between 40:1            and 1:40;        -   b) the molar ratio oft to s is in the range of between 40:1            and 1:40; or        -   c) combinations thereof.

In an aspect of the invention, the one or more star macromoleculesrepresented by Formula (I) may comprise a two-arm type of starmacromolecule, such as when t=0. In another aspect of the invention, theone or more star macromolecules represented by Formula (I) may comprisea three-arm type of star macromolecule, such as when t=1 or greater(that is when t is present).

In an aspect of the invention, the hydroxyl-containing copolymericsegment P4 of Formula (I) may comprise repeat units of monomericresidues of polymerized monomers, wherein at least one of the monomericresidues, such as 2, 3, 4, 5 or 6 or more of the monomeric residues, ora plurality of the monomeric residues, is a hydroxyl-containingmonomeric residue, and at least one of the monomeric residues or aplurality of the monomeric residues is a hydrophobic monomeric residue.For example, the hydroxyl-containing copolymeric segment P4 of Formula(I) may have hydrophobic characteristics and hydroxyl-containingcharacteristics, such that P4 may comprise predominantly, substantially,or mostly polymerized hydrophobic monomeric residues and at least one ora plurality of polymerized hydroxyl-containing monomeric residues. In anaspect of the invention, the hydroxyl-containing copolymeric segment P4of Formula (I) may comprise repeat units of monomeric residues ofpolymerized monomers, wherein at least one of the monomeric residues ora plurality of the monomeric residues is a hydroxyl-containing monomericresidue, and at least one of the monomeric residues or a plurality ofthe monomeric residues is a hydrophilic monomeric residue. For example,the hydroxyl-containing copolymeric segment P4 of Formula (I) may havehydrophilic characteristics and hydroxyl-containing characteristics,such that P4 may comprise predominantly, substantially, or mostlypolymerized hydrophilic monomeric residues and at least one or aplurality of polymerized hydroxyl-containing monomeric residues.

In one aspect of the invention, a star macromolecule of Formula (I) iscapable of thickening via a dual mechanism comprising (1) self-assemblyof the hydrophobic polymerized segments of the star macromolecules viahydrophobic interactions or associations, and (2) association, reaction,or combination of the hydroxyl-containing polymerized segments of one ormore of the star macromolecules with one or more thickening crosslinkingagents, such as boric acid or borate-type additives, for example viaesterification of at least one hydroxyl-containing monomeric residuewithin the hydroxyl-containing polymerized segments of one or more starmacromolecules with the thickening crosslinking agents (e.g., boric acidor borate-type additive), such as esterification of at least onehydroxyl-containing monomeric residue within the hydroxyl-containingpolymerized segments of a first star macromolecule with the thickeningcrosslinking agents (e.g., boric acid or borate-type additive), andesterification of at least one hydroxyl-containing monomeric residuewithin the hydroxyl-containing polymerized segments of a second starmacromolecule with said thickening crosslinking agents (e.g., boric acidor borate-type additive).

Polymer compositions comprising the star macromolecules of Formula (I)may be suitable for use in hydraulic fracturing fluids.

The star macromolecules of Formula (I) may be suitable for use asthickening agents, use as rheology modifiers, use in fracturing fluids,use in mining applications, providing salt tolerancy, use in cosmeticand personal care applications, use in home care applications, use inadhesive applications, use in electronic applications, use in medicaland pharmaceutical applications, use in paper applications, or use inagricultural applications.

In one aspect the invention provides a polymer composition comprisingstar macromolecules of Formula (I), each star macromolecule having acore and may have five or more arms, wherein the number of arms within astar macromolecule varies across the composition of star molecules; andthe arms on a star are covalently attached to the core of the star; eacharm comprises one or more (co)polymer segments; and at least one armand/or at least one segment exhibits a different solubility from atleast one other arm or one other segment, respectively, in a referenceliquid of interest.

In one aspect of the invention, the star macromolecules of Formula (I),gel and/or thickening agent, including those formed by a one-potprocess, ATRP, CRP, and/or combinations of one or more of theseprocesses, may be used to provide a certain level of control overviscosity and consistency factors in many aqueous and oil based systemsincluding, for example, fracturing fluid additives, gelling agents,gels, proppant stabilizers, breakers, friction reducers, thickeningagents.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in oil and gas applications, including but notlimited to, as rheology modifiers for fracturing fluids/drilling wellfluids, gelling agents, gels, dispersants, proppant stabilizers andcarriers, breakers, friction reducers, lubricants, scale-buildupinhibitors, heat transfer fluids, thickening agents, additives toimprove oil extraction from oil sands, emulsion breakers foroil-sand-water emulsions, or additives to improve dewatering of oilsands.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in mining applications, including but not limitedto, dust suppressants, flocculating agents, gold and precious metalextraction, and precious metal processing, lubricants and drag reductionagents for pipeline slurry transport.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in cosmetic and personal care applications,including but not limited to, cosmetic creams, lotions, gels, sprayablelotion, sprayable cream, sprayable gel, hair styling sprays and mousses,hair conditioners, shampoos, bath preparations, ointments, deodorants,mascara, blush, lip stick, perfumes, powders, serums, skin cleansers,skin conditioners, skin emollients, skin moisturizers, skin wipes,sunscreens, shaving preparations, solids, and fabric softeners.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in home care applications, including but not limitedto, cleaners for windows and glass, and other household surfaces, toiletareas, enzyme production, drain cleaners, liquid and gelled soaps,polishes and waxes, liquid and powdered detergents including detergentsfor laundry and in dish washing.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in adhesive applications, including but not limitedto, associative complexes, billboard adhesives, carpet backsizingcompounds, hot melt adhesives, labeling adhesives, latex adhesives,leather processing adhesives, plywood laminating adhesives, paperadhesives, wallpaper pastes, wood glue.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in electronic applications, including but notlimited to, antistatic film and packaging, conductive inks, rheologycontrol agents used for copper foil production, multilayer ceramic chipcapacitors, photoresists, plasma display screens, lubricants for wire,cable, and optical fibers, gel lacquers for coil coating.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in medical and pharmaceutical applications,including but not limited to, but not limited to, medical devicelubrication, antibacterial coatings, pharmaceutical excipients such asbinders, diluents, fillers, lubricants, glidants, disintegrants, polishagents, suspending agents, dispersing agents, plasticizers.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in paper applications, including but not limited to,coatings, dispersion for tissue and thin papers, filler retention anddrainage enhancement, flocculation and pitch control, grease-proofcoatings, adhesives, release coatings, surface sizing, sizes for glossand ink holdout, tail tie and pickup adhesives for papermaking.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in agricultural applications, including but notlimited to, animal feed, dispersing agents, drift control,encapsulation, seed coatings, seed tape, spray adherents, water-basedsprays and spray emulsions, water-soluble packaging.

In another aspect of the invention, the star macromolecules of Formula(I) may be suitable in other applications including but not limited to,water- and solvent-based coating compositions, water- and solvent-basedlubricants, water- and solvent-based viscosity index modifiers, paints,plasticizers, antifoaming agents, antifreeze substances, corrosioninhibitors, detergents, dental impression materials, dental fillers,inkjet printer ink and other inks, ceramic and brick forming,prepolymers such as polyols for use in polyesters, polyurethanes,polycarbonates. For rheology modifier applications, characteristics arehigh gel strength, stability in the presence of salt and increasedtemperatures, high shear thinning characteristics, forms versatile lowviscosity soluble concentrations, and synergistic interactions withadded agents to adjust their rheology profile to optimize propertiessuch as sedimentation, flow and leveling, sagging, spattering, etc.

In one aspect of the invention, there is a star macromolecule having amolecular weight of between 150,000 g/mol and 5,000,000 g/mol that formsa clear homogeneous gel when dissolved in water at a concentration of atleast 0.05 wt. % wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) the dynamic viscosity increases after addition of a        thickening crosslinking agent; and/or    -   iii) a shear-thinning value of at least 5.

In one aspect of the invention, there is a star macromolecule having amolecular weight of between 150,000 g/mol and 5,000,000 g/mol that formsa clear homogeneous gel when dissolved in water at a concentration of atleast 0.05 wt. % wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) the dynamic viscosity increases after addition of boric        acids, boronic acid, borates, borate derivatives thereof, or        borate-type additives; and/or    -   iii) a shear-thinning value of at least 5.

In one aspect of the invention, there is a star macromolecule having amolecular weight of between 150,000 g/mol and 5,000,000 g/mol that formsa clear homogeneous gel when dissolved in water at a concentration of atleast 0.05 wt. % wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) the dynamic viscosity increases after addition of a        thickening crosslinking agent;    -   iii) a salt-induced break value of at least 50%;    -   iv) a pH-induced break value of at least 50%;    -   v) a shear-thinning value of at least 5; or    -   vi) combinations thereof.

In one aspect of the invention, there is a clear homogeneous gel,comprising a star macromolecule having a molecular weight of between150,000 g/mol and 5,000,000 g/mol, comprises the following properties:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) the dynamic viscosity increases after addition of a        thickening crosslinking agent;    -   iii) a salt-induced break value of at least 50%;    -   iv) a pH-induced break value of at least 50%; and/or    -   v) a shear-thinning value of at least 10;        wherein the gel is formed when the star macromolecule is        dissolved in water at a concentration of at least 0.05 wt. %.

In one aspect of the invention, there is a clear homogeneous gel,comprising a star macromolecule having a molecular weight of between150,000 g/mol and 5,000,000 g/mol, comprises the following properties:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) the dynamic viscosity increases after addition of boric        acids, boronic acid, borates, borate derivatives thereof, or        borate-type additives;    -   iii) a salt-induced break value of at least 50%;    -   iv) a pH-induced break value of at least 50%;    -   v) a shear-thinning value of at least 10; and/or    -   vi) an emulsion value of >12 hours;        wherein the gel is formed when the star macromolecule is        dissolved in water at a concentration of at least 0.05 wt. %.

In one aspect of the invention, there is an emulsifier-free emulsioncomprising:

a water-soluble star macromolecule having:

-   -   i) molecular weight of at least 150,000 g/mol; and    -   ii) a dynamic viscosity of at least 20,000 cP at a concentration        of 0.4 wt. %.

In one aspect of the invention, there is an emulsion comprising:

a water-soluble star macromolecule having:

-   -   i) a molecular weight of at least 150,000 g/mol; and    -   ii) a dynamic viscosity of at least 20,000 cP at a concentration        of 0.4 wt. %.

In one aspect of the invention, there is a thickening agent that forms aclear homogeneous gel when dissolved in water at a concentration of atleast 0.2 wt. %, wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a pH-induced break value of at least 80%;    -   iv) a shear-thinning value of at least 10; and/or    -   v) an emulsion value of greater than 12 hours.

In one aspect of the invention, the star macromolecule, emulsifier, gel,emulsifier-free emulsion, emulsion and/or thickening agent, includingthose formed by the one-pot process, ATRP, CRP, RAFT, TEMPO, Nitroxide,LRP, CRP, anionic polymerization and cationic polymerization, and/orcombinations of one or more of these processes, may be used to provide acertain level of control over viscosity and consistency factors in manyaqueous and oil based systems including, for example, hydraulicfracturing fluid additives, gelling agents, gels, proppant stabilizers,breakers, friction reducers, thickening agents.

Other applications may include water- and solvent-based coatingcompositions, paints, detergents, cleaners, inks, antifoaming agents,antifreeze substances, corrosion inhibitors, detergents, oil-welldrilling-fluid rheology modifiers, and additives to improve waterflooding during enhanced oil recovery.

In one aspect of the invention, there is a macromolecule, comprising: aplurality of arms comprising at least three types of arms, wherein afirst-arm-type extends beyond a second-arm-type and said first-arm-typehas a hydrophobic segment on its distal end, wherein at least a portionof the hydrophobic segment may extend beyond the length of thesecond-arm-types either by the size of the monomeric segment or segments(which may be varied by length of monomeric residue, degree ofpolymerization, and/or both) for which the hydrophobic segment isattached; and wherein a third-arm-type extends beyond a second-arm-typeand said third-arm-type has a hydroxyl-containing segment (homopolymericor copolymeric) on its distal end, wherein at least a portion of thehydroxyl-containing segment (homopolymeric or copolymeric) may extendbeyond the length of the second-arm-types either by the size of themonomeric segment or segments (which may be varied by length ofmonomeric residue, degree of polymerization, and/or both) for which thehydroxyl-containing segment (homopolymeric or copolymeric) is attached.

Recognizing that the “length” of an arm or segment and the “extendingbeyond” limitation may be theoretical, meaning that while it is notempirically measured it is understood to “extend beyond” and/or have alonger “length” relative to the length of the second-arm-type if thedegree of polymerization is greater for monomeric residues of the sametype or of the same theoretical length.

In one aspect of the invention, there is a star macromolecule,comprising: a plurality of arms comprising at least three types of arms,wherein the degree of polymerization of a first-arm-type and athird-arm-type are greater than the degree of polymerization of asecond-arm-type, and wherein said first-arm-type and said third-arm-typehave a distal end portion that is hydrophobic and hydroxyl-containing,respectively. In another aspect of the invention, this starmacromolecule may be formed by first forming or obtaining thehydrophobic portion and the hydroxyl-containing portion then forming theremaining portion of the first-arm-type from the end of the hydrophobic,the third-arm-type from the end of the hydroxyl-containing portion, andthe second-arm-type, in a one-pot synthesis, wherein the polymerizationof the second portion of the first-arm-type and the second portion ofthe third-arm-type are commenced prior to the initialization of thesecond-arm-type but there is at least some point wherein portions, e.g.,substantial portions, of the first-arm-type, third-arm-type, andsecond-arm-type are being polymerically extended simultaneously. Incertain embodiments, the hydroxyl-containing copolymeric arm may extendbeyond the distal end of the hydrophobic containing copolymeric arm. Incertain embodiments, the hydroxyl-containing copolymeric arm may have agreater degree of polymerization than the hydrophobic containingcopolymeric arm.

In one aspect of the invention, there is an oil-soluble starmacromolecule, comprising: a plurality of different arms comprising atleast three types of arms, wherein a first-arm-type extends beyond asecond-arm-type and said first-arm-type has a hydrophilic segment on itsdistal end, and wherein a third-arm-type extends beyond thesecond-arm-type and said third-arm-type has a hydroxyl-containingsegment (homopolymeric or copolymeric) on its distal end.

In one aspect of the invention, there is an oil-soluble starmacromolecule, comprising: a plurality of arms comprising at least threetypes of arms, wherein the degree of polymerization of a first-arm-typeis greater than the degree of polymerization of a second-arm-type, andwherein said first-arm-type has a hydrophilic segment on its distal end,and wherein the degree of polymerization of a third-arm-type is greaterthan the degree of polymerization of the second-arm-type, and whereinsaid third-arm-type has a hydroxyl-containing segment (homopolymeric orcopolymeric) on its distal end.

In one aspect of the invention, there is a star macromolecule,comprising: a plurality of arms comprising at least three types of arms,wherein the degree of polymerization of a first-arm-type andthird-arm-type are greater than the degree of polymerization of asecond-arm-type, and wherein said first-arm-type and third-arm-type havea distal end portion that is hydrophobic and hydroxyl-containing,respectively, and the proximal portion of the first-arm-type and thethird-arm-type and the second-arm-type are the same with the onlydifference between the first-arm-type and the third-arm-type and thesecond-arm-type being that the first-arm-type and the third-arm-typehave a hydrophobic and hydroxyl-containing containing portion on theirdistal ends, respectively. In another aspect of the invention, this starmacromolecule may be formed by first forming or obtaining thehydrophobic portion and the hydroxyl-containing portions and thenforming the remaining portion of the first-arm-type and third-arm-typefrom the end of the hydrophobic and hydroxyl-containing portion,respectively, and the second-arm-type simultaneously in a one-potsynthesis.

In an aspect of the invention, the star macromolecules may have an HLBof greater than 0.85, for example greater than 0.87. or 0.9 or 0.93 or0.95 or 0.97 or 0.98.

In an aspect of the invention, the star macromolecules may have acalculated HLB of greater than 0.85, for example greater than 0.87. or0.9 or 0.93 or 0.95 or 0.97 or 0.98 and a viscosity of greater than60,000 cP at a pH between 7 to 10.5 and a molecular weight of between200,000 g/mol and 550,000 g/mol and a shear-thinning value of at least10 and, optionally, a salt-induced break value of at least 60%.

In an aspect of the invention, the star macromolecule may be a three-armtype star macromolecule and may have a sum total number of arms (r+s) ofbetween 3 and 1000, or a sum total number of arms (s+t) of between 3 and1000, or a sum total number of arms (r+t) of between 3 and 1000, orcombinations thereof. In an aspect of the invention, the starmacromolecule may be a two-arm type star macromolecule and may have asum total number of arms (r+s) of between 3 and 1000.

In an aspect of the invention, the star macromolecule may be a three-armtype star macromolecule and may have a sum total number of arms (r+s) ofbetween 3 and 500, or a sum total number of arms (s+t) of between 3 and500, or a sum total number of arms (r+t) of between 3 and 500, orcombinations thereof. In an aspect of the invention, the starmacromolecule may be a two-arm type star macromolecule and may have asum total number of arms (r+s) of between 3 and 500.

In an aspect of the invention, the star macromolecule may have a sumtotal number of arms (r+t) of between 15 and 45, or a sum total numberof arms (s+t) of between 15 and 45, or both a sum total number of arms(r+t) and a sum total number of arms (s+t) of each between 15 and 45.

In an aspect of the invention, the star macromolecule may be a two-armtype star macromolecule (e.g., when t=0) and may have a molar ratio of rto s in the range of between 40:1 and 1:40. In an aspect of theinvention, the star macromolecule may be a three-arm type starmacromolecule (e.g., when t is at least 1 or greater) and may have amolar ratio of r to sin the range of between 40:1 and 1:40, a molarratio of r to t in the range of between 40:1 and 1:40, or a molar ratioof s to t in the range of between 40:1 and 1:40, or combinationsthereof.

In an aspect of the invention, the star macromolecule may have a molarratio of r to t in the range of between 8:1 and 3:1, or a molar ratio ofs to t in the range of between 8:1 and 3:1, or both a molar ratio of rto t and a molar ratio of s to t each in the range of between 8:1 and3:1.

In an aspect of the invention, the star macromolecule of Formula (I) mayhave both q2 and q3 may have a value greater than 100, and q2 is greaterthan q3; or both q5 and q3 may have a value greater than 100, and q5 isgreater than q3; or both q2 and q3 may have a value greater than 100,and q5 and q3 have a value greater than 100, and q2 and q5 are greaterthan q3.

In an aspect of the invention, the arms represented by[(P1)_(q1)-(P2)_(q2)] and [(P4)_(q4)-(P5)_(q5)] of star macromolecule ofFormula (I) may have an HLB value greater than 18, e.g., greater than19.

In an aspect of the invention, the P1 polymeric segment of starmacromolecule of Formula (I) may be a predominantly hydrophobicpolymeric segment having an HLB value of less than 8.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP; and/or    -   ii) a shear-thinning value of at least 10.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   i) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; or    -   iv) combinations thereof.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 600,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; or    -   iv) combinations thereof;        wherein the gel-forming star macromolecule may further have a        viscosity of greater than 40,000 cP at a pH between 6 to 11.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; and/or    -   iv) an emulsion value of greater than 12 hours.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 600,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; and/or    -   iv) an emulsion value of greater than 12 hours;        wherein the gel-forming star macromolecule may further have a        viscosity of greater than 40,000 cP at a pH between 6 to 11.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP; and/or    -   ii) a shear-thinning value of at least 10;        wherein the gel-forming star macromolecule may further have a        viscosity of less than 5,000 cP at a shear rate of 4 sec⁻¹.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a shear-thinning value of at least 10; and/or    -   iii) a salt-induced break value of at least 60%;        wherein the gel-forming star macromolecule may further have a        viscosity of less than 5,000 cP at a shear rate of 4 sec⁻¹.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; or    -   iv) combinations thereof;        wherein the gel-forming star macromolecule may further have a        viscosity of less than 5,000 cP at a shear rate of 4 sec⁻¹.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; or    -   iv) combinations thereof;        wherein the gel-forming star macromolecule may further have a        PDI of less than 2.5.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; or    -   iv) combinations thereof;        wherein the gel-forming star macromolecule may have between 15        to 45 arms.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP; and/or    -   ii) a shear-thinning value of at least 10;        wherein the arms of the gel-forming star macromolecule may        further comprise:    -   i) hydrophilic homopolymeric arms;    -   ii) copolymeric arms, comprising:        -   a) hydrophilic polymeric segments and hydrophobic polymeric            segments; and        -   b) hydrophilic polymeric segments and copolymeric segment            comprising polymerized hydroxyl-containing monomeric            residues and hydrophobic monomeric residues.

In an aspect of the invention, a dual-mechanism thickening agent maycomprise a star macromolecule having a molecular weight of between150,000 g/mol and 1,000,000 g/mol that forms a homogeneous gel whendissolved in water at a concentration of at least 0.05 wt. %;

wherein the gel has:

-   -   i) a dynamic viscosity of at least 20,000 cP;    -   ii) a salt-induced break value of at least 60%;    -   iii) a shear-thinning value of at least 10; or    -   iv) combinations thereof;        wherein the arms of the gel-forming star macromolecule may        further comprise:    -   i) hydrophilic homopolymeric arms;    -   ii) copolymeric arms, comprising: a) hydrophilic polymeric        segments and hydrophobic polymeric segments; and b) hydrophilic        polymeric segments and hydroxyl-containing polymeric segments.

In an aspect of the invention, a fracturing fluid composition,comprising at least 0.05 wt. % of a dual-mechanism thickening agent toimprove water flooding during enhanced oil recovery, wherein thedual-mechanism thickening agent is a star macromolecule comprising:

-   -   a) a molecular weight of greater than 100,000 g/mol;    -   b) a core having a hydrophobic crosslinked polymeric segment;        and    -   c) a plurality of arms comprising at least three types of arms,        wherein:        -   i) a first-arm-type extends beyond a second-arm-type, and            said first-arm-type has a hydrophobic segment on its distal            end; and        -   ii) a third-arm-type extends beyond a second-arm-type, and            said third-arm-type has a hydroxyl-containing segment on its            distal end;            wherein the rheology-modifying composition has a            shear-thinning value of at least 6.

In an aspect of the invention, a fracturing fluid composition,comprising at least 0.05 wt. % of a dual-mechanism thickening agent toimprove water flooding during enhanced oil recovery, wherein thedual-mechanism thickening agent is a star macromolecule comprising:

-   -   a) a molecular weight of greater than 100,000 g/mol;    -   b) a core having a hydrophobic crosslinked polymeric segment;        and    -   c) a plurality of arms comprising at least three types of arms,        wherein:        -   i) a first-arm-type extends beyond a second-arm-type, and            said first-arm-type is a copolymeric arm having a            hydrophobic polymeric segment on its distal end; and        -   ii) a third-arm-type extends beyond the second-arm-type, and            said third-arm-type is a copolymeric arm having a            hydroxyl-containing polymeric segment on its distal end;            wherein the rheology-modifying composition has a            shear-thinning value of at least 6.

In an aspect of the invention, a fracturing fluid composition,comprising at least 0.05 wt. % of a dual-mechanism thickening agent toimprove water flooding during enhanced oil recovery, wherein thedual-mechanism thickening agent is a star macromolecule comprising:

-   -   a) a molecular weight of greater than 100,000 g/mol;    -   b) a core having a hydrophobic crosslinked polymeric segment;        and    -   c) a plurality of arms comprising at least three types of arms,        wherein:        -   i) a first-arm-type extends beyond a second-arm-type, and            said first-arm-type has a hydrophobic segment on its distal            end; and        -   ii) a third-arm-type extends beyond a second-arm-type, and            said third-arm-type has a hydroxyl-containing segment on its            distal end;            wherein the rheology-modifying composition has a            shear-thinning value of at least 6; and wherein the            composition may further comprise one or more boric acid or            borate-type additives.

BRIEF DESCRIPTION OF THE FIGURES

The following figures exemplify aspects of the disclosed process but donot limit the scope of the process to the examples discussed.

FIG. 1: is a schematic representation of an embodiment of a three-armtype star macromolecule in accordance with of Formula (I), wherein “HB”represents a hydrophobic polymeric segment, “HP” represents ahydrophilic polymeric segment, and “HO” represents a hydroxyl-containingpolymeric segment.

FIG. 2: GPC curve of the ((MMA)₁₅-co-(GMA)₂) macroinitiator in step 1,the block copolymer arms [((MMA)₁₅-co-(GMA)₂)-(tBA)₂₈₇], the mixture ofblock copolymer arms [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇] and homopolymer arms[(tBA)₂₀], and the [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] starmacromolecule (r to s is 3:1) in the synthesis of an exemplary[((MMA)₁₅-co-(GMA)₂)-(AA)₃₀₇]/[(AA)₂₀] star macromolecule (r to s is3:1).

FIG. 3: is a graph of viscosity vs. shear rate of aqueous solution of0.6 wt. % of [((MMA)₁₅-co-(GMA)₂)-(AA)₃₀₇]/[(AA)₂₀] star macromolecule(r to s is 3:1) (from Example 1).

DETAILED DESCRIPTION OF THE INVENTION

The term “solubility” or “soluble” is understood to mean that when acomponent is mixed into a solvent and tested, at STP in a 1 cm cuvette,it has a light transmittance value, at a wavelength at or around aUV/Vis minimum wavelength for the mixture, of at least 40%, for example,at least 50%, 70%, 85%, or at least 95%.

The term “clear” as is used to describe a homogenous gel or homogenoussolution is understood to mean that when the gel or solution is tested,at STP in a 1 cm cuvette, it has a light transmittance value, at awavelength at or around a UV/Vis minimum wavelength for the gel orsolution, of at least 40%, for example, at least 50%, 70%, 85%, or atleast 95%.

The term “water-soluble monomer” is understood to mean a monomer havingat least about 10 wt. % solubility in water at STP. For example, a watersoluble monomer may have at least 15 wt. %, 20 wt. %, 25 wt. %, or atleast 30 wt. % solubility in water at STP.

The term “water-insoluble monomer” is understood to mean a monomerhaving less water solubility than a water soluble monomer, for example,less that about 5 wt. %, such as less than 1 wt. % or 0.5 wt. %solubility in water at STP.

The term “water-soluble star macromolecule” is understood to mean a starmacromolecule that is soluble in water, pH adjusted if necessary to a pHof no greater than 8 with sodium hydroxide, at a concentration of atleast 5 g/L, for example, between 8 g/L to 100 g/L, such as, at least 10g/L, 12 g/L, 15 g/L, or at least 20 g/L. For example, a water-solublestar macromolecule having an aqueous solubility of at least 10 g/L mayinclude the introduction of at least 10 g of the star macromolecule intoapproximately 1 L of water, neutralizing the mixture, if necessary, byadjusting the pH of the resulting mixture to about pH 8 (e.g., with theaddition of base, such as sodium hydroxide), and vigorously stirring ata temperature no greater than 100° C. for no more than about 60 minutes,to achieve dissolution of the star macromolecule, and testing thesolubility at STP.

The term “oil-soluble star macromolecule” is understood to mean a starmacromolecule that is soluble in mineral oil at a concentration of atleast 5 g/L, for example, between 8 g/L to 100 g/L, such as, at least 10g/L, 12 g/L, 15 g/L, or at least 20 g/L of mineral oil. For example, anoil-soluble star macromolecule having an oil solubility of at least 10g/L may include the introduction of at least 10 g of the starmacromolecule into approximately 1 L of mineral oil, and vigorouslystirring at a temperature no greater than 100° C. for no more than about60 minutes, to achieve dissolution of the star macromolecule, andtesting the solubility at STP.

The term “hydrophilic” is understood to mean, in relation to a material,such as a polymeric arm, or a polymeric segment of a polymeric arm, thatthe material is water soluble and comprises hydrophilic segments havingan HLB equal to or greater than 8, for example, an HLB equal to 16-20,or equal to or greater than 18, 19, or 19.5. In certain embodiments, thehydrophilic segment may comprise at least 75 mol % of water-solublemonomer residues, for example, between 80 mol % to 100 mol % or at least85 mol %, 90 mol %, 95 mol %, or at least 97 mol % water-soluble monomerresidues.

The term “hydrophobic” is understood to mean, in relation to a material,such as a polymeric arm, or a polymeric segment of a polymeric arm, thatthe material is water insoluble and comprises hydrophilic segmentshaving an HLB less than 8, for example, an HLB less than 7. In certainembodiments, the hydrophobic segment may comprise at least 75 mol % ofwater-insoluble monomer residues, for example, between 80 mol % to 100mol % or at least 85 mol %, 90 mol %, 95 mol %, or at least 97 mol %water-insoluble monomer residues.

The term “monomer residue” or “monomeric residue” is understood to meanthe residue resulting from the polymerization of the correspondingmonomer. For example, a polymer derived from the polymerization of anacrylic acid monomer (or derivatives thereof, such as acid protectedderivatives of acrylic acid including but not limited to methyl ort-butyl ester of acrylic acid), will provide polymeric segments,identified as PAA, comprising repeat units of monomeric residues ofacrylic acid, i.e., “—CH(CO₂H)CH₂—”. For example, a polymer derived fromthe polymerization of styrene monomers will provide polymeric segments,identified as PS, comprising repeat units of monomeric residues ofstyrene, i.e., “—CH(C₆H₅)CH₂—.” For example, a polymer derived from thepolymerization of monomeric divinylbenzene monomers will providepolymeric segments comprising repeat units of monomeric residues ofdivinylbenzene, i.e., “—CH₂CH(C₆H₅)CHCH₂—.”

The term “emulsifier” is understood to mean a component that comprisesan appreciable weight percent of an amphiphilic compound having amolecular weight of less than 5,000 MW. Emulsifiers are usually linearorganic compounds that contain both hydrophobic portions (tails) andhydrophilic portions (heads), i.e., are amphiphilic. Examples ofemulsifiers include but are not limited to: alkyl benzenesulfonates,alkanesulfonates, olefin sulfonates, alkyl ethersulfonates, glycerolether sulfonates, alpha-methyl ester sulfonates, sulfofatty acids, alkylsulfates, fatty alcohol ether sulfates, glycerol ether sulfates, hydroxymixed ether sulfates, monoglyceride (ether) sulfates, fatty acid amide(ether) sulfates, mono- and dialkylsulfosuccinates, mono- anddialkylsulfosuccinamates, sulfotriglycerides, ether carboxylic acids andsalts thereof, fatty acid isethionates, fatty acid sarcosinates, fattyacid taurides, acyl lactylates, acyl tartrates, acyl glutamates, acylaspartates, alkyl oligoglucoside sulfates, protein fatty acidcondensates (particularly wheat-based vegetable products) and alkyl(ether) phosphates, alkylbetaines, alkylamidobetaines, aminopropionates,aminoglycinates, imidazoliniumbetaines and sulfobetaines.

The term “emulsifier-free” is understood to mean a composition ormixture wherein the formulation is substantially devoid of anyemulsifiers, for example less than 0.1 wt. % of emulsifier, relative tothe total composition, or less than 0.05 wt. % of emulsifier, relativeto the total composition, or less than 0.01 wt. % of emulsifier,relative to the total composition, or a formulation where there is noemulsifier.

The term “STP” is understood to mean standard conditions for temperatureand pressure for experimental measurements, wherein the standardtemperature is a temperature of 25° C. and the standard pressure is apressure of 1 atm.

The term “hydroxyl” and “hydroxy” is understood to mean the functionalgroup —OH. The term “hydroxyl-containing” or “hydroxy-containing” isunderstood to mean any monomer, polymer or molecules which have a —OHfunctional group.

The term “boric acid” or “boronic acid” is understood to mean anyadditive included in hydraulic fracturing fluids which may contain,release, or evolve, boric acid or compounds which act in the same manneras boric acid (“borate-type” or “borate-type additive” or “borate-typecrosslinker”), that is to complex, interact, or crosslink with thehydroxyl-containing polymeric segment, such as a third-arm-type, toimpart temporary or permanent crosslinking or increased viscosity.

Structure of the Polymer Composition

As used herein, the term “reference liquid of interest” means the liquidto which the polymer composition will be added. Suitable examples ofreference liquids include, but are not limited to, water, oil or mixturethereof or water with additives which include but are not limited to;surfactants, oils, fats and waxes, emulsifiers, silicone compounds, UVprotectors, antioxidants, various water soluble substances, biogenicagents, and enzyme inhibitors. Such agents are disclosed in U.S. Pat.Nos. 6,663,855 and 7,318,929 and are herein incorporated by reference toprovide definitions for those terms.

Monomer units within the arms may be connected with C—C covalent bonds.This is believed to make them hard to degrade so that the starmacromolecule may perform as efficient thickening agent in a harshenvironment (very high/low pH or in the presence of strong oxidizingagents).

Suitable crosslinkers for the core encompass all of the compounds whichare capable, under the polymerization conditions, of bringing aboutcrosslinking. These include but are not limited di-, tri-,tetra-functional (meth)acrylates, di-, tri- and tetra-functionalstyrenes and other multi- or poly-functional crosslinkers.

Some examples of the crosslinking agents may include but are not limitedto 1,2-divinylbenzene, 1,3-divinylbenzene and 1,4-divinylbenzene,1,2-ethanediol di(meth)acrylate, 1,3-propanediol di(meth)acrylate,1,4-butanediol di(meth)acrylate, 1,5-hexanediol di(meth)acrylate,divinylbenzene, ethyleneglycol di(meth)acrylate, propyleneglycoldi(meth)acrylate, butyleneglycol di(meth)acrylate, triethyleneglycoldi(meth)acrylate, polyethyleneglycol di(meth)acrylate,polypropyleneglycol di(meth)acrylate, polybutyleneglycoldi(meth)acrylate, and allyl(meth)acrylate, glycerol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, allyl methacrylate, allyl acrylate.

The terms ‘mostly soluble’, ‘not fully soluble’, and ‘not soluble’ areused to describe the extent which a composition which is capable ofbeing dissolved in a reference liquid of interest.

The term ‘mostly soluble’ is used to describe a composition which iscapable dissolves completely with exception of a slight cloudiness inthe reference liquid of interest. The term ‘not fully soluble’ is usedto describe a composition which disperses with a cloudiness in thereference liquid of interest. The term ‘not soluble’ is used to describea composition which does not disperse and remains as a solid in thereference liquid of interest. A list of solvents and non-solvent forpolymers can be found in “Polymer Handbook, 4^(th) Ed.” edited byBrandrup J.; Immergut, Edmund H.; Grulke, Eric A.; Abe, Akihiro; Bloch,Daniel R., John Wiley & Sons: 2005.

An embodiment of the present invention can be exemplified by a multi-armstar macromolecule wherein the average number of arms in the starmacromolecule is between 5 and 500, preferentially between 10 and 250.

In one embodiment, the star macromolecule has a core which containsadditional functionality and/or expanded free volume. ‘Expended freevolume’ of the core is defined as the core with lower crosslink density.The free volume in the core is generated when during the crosslinkingprocess of crosslinker with monomer P2 and/or with monomer P5, orcrosslinker is used. If P2, P5, or crosslinkers, are monomers withfunctional groups, these groups will be incorporated in the core.

In one embodiment, the star macromolecule may store and release incontrolled rate the small molecules. ‘Small molecules’ are UV absorbers,minerals, dyes, pigments, solvents, surfactants, metal ions, salts, oroils. These small molecules can be stored inside the core of the starmacromolecule and next released. Each small molecule has some affinityto the core, is soluble in the core environment. Higher affinity of thesmall molecule to the core will result in the lower rate of release fromstar macromolecule. The affinity may be increased or decreased throughnon-covalent forces including H-bonding, electrostatic, hydrophobic,coordination and metal chelating interactions.

In one embodiment, the star macromolecule displays shear thinningbehavior. ‘Shear thinning’ is defined as an effect where viscositydecreases with increasing rate of shear stress. The extent of shearthinning behavior is characterized using a Brookfield-type viscometerwhere viscosities are measured under different shear rates.

In one embodiment, the star macromolecule arms comprise a (co)polymersegment that exhibits an upper, or higher, critical solution temperature(UCST or HCST) whereby the star macromolecule is soluble in a liquid athigher temperature, say above 44° C., then at the lower use temperaturethe outer shell polymer segments become insoluble and self assemble toform a shear sensitive gel or in another embodiment the invention theouter shell of the star macromolecule arms comprise a (co)polymersegment that exhibits a lower critical solution temperature (LCST), say5° C., whereby the star macromolecule is soluble in a liquid at lowertemperature then at the use temperature the outer shell polymer segmentsbecome insoluble and self assemble to form a shear sensitive gel. In thecase of a LCST it is envisioned that a copolymer segment with an LCSTbelow 10° C., preferable below 5° C. would be optimal. A non-limitingexample would be a copolymerization of BuMA and DMAEMA and preparationof copolymers with designed LCST. A copolymer with 10% BuMA has a LCSTclose to 0° C. and one would use less BuMA or a less hydrophobic monomersuch as MMA to increase the LCST to ˜5° C. Indeed the Tg of the segmentof the star can be selected to allow dissolution of the star in roomtemperature aqueous media.

Therefore in a in a non-limiting example the stars comprise acrosslinked core, and arms comprising an water soluble polymeric segment(e.g. poly(acrylic acid), poly(2-hydroxyethyl acrylate),poly(N-isopropylacrylamide), poly(ethylene glycol) methacrylate,quaternized poly(dimethylaminoethyl methacrylate), etc.) and ahydrophobic polymeric segment (e.g. polystyrene or substitutedpolystyrenes, poly(alkyl(meth)acrylate), etc.) or a hydrocarbon-basedsegment. Suitable hydrocarbon-based segments can comprise low molecularweight α-olefin. Lower molecular weight α-olefins are commerciallyavailable and higher molecular weight species can be prepared bytelomerization of ethylene or ethylene propylene mixtures. [Kaneyoshi,H.; Inoue, Y.; Matyjaszewski, K. Macromolecules 2005, 38, 5425-5435.]

In an embodiment, the polymer compositions can self assemble in solutionto provide a certain level of control over viscosity and consistencyfactors in many aqueous and oil based systems where control over therheology is a concern. Applications include; water- and solvent-basedcoating compositions, paints, inks, anti foaming agents, antifreezesubstances, corrosion inhibitors, detergents, oil-well drilling-fluidrheology modifiers, hydraulic fracturing fluid thickening agents, oradditives to improve water flooding during enhanced oil recovery, withthe rheology modifier providing characteristics of high gel strength,highly shear thinning characteristics, forms versatile low viscositysoluble concentrations, and synergistic interactions with added agentsto adjust their rheology profile to optimize properties such assedimentation, flow and leveling, sagging, spattering, etc.

In certain embodiments, one or more star macromolecules of the presentinvention may be prepared by an improved, efficient arm-firstliving-controlled radical polymerization method, wherein the one or morestar macromolecules are represented by Formula (I):

wherein:

-   -   Core represents a crosslinked polymeric segment;    -   P1 represents a hydrophobic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophobic monomers;    -   P2 represents a hydrophilic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophilic monomers;    -   P3 represents a hydrophilic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophilic monomers;    -   P4 represents a hydroxyl-containing segment (homopolymeric or        copolymeric) comprised of repeat units of monomeric residues,        where at least one of the monomeric residues or a plurality of        the monomeric residues is a hydroxyl-containing monomeric        residue, of polymerized monomers;    -   P5 represents a hydrophilic polymeric segment comprised        predominantly of repeat units of monomeric residues of        polymerized hydrophilic monomers;    -   q1 represents the number of repeat units in P1 and has a value        between 1 and 50;    -   q2 represents the number of repeat units in P2 and has a value        between 30 and 2000;    -   q3 represents the number of repeat units in P3 and has a value        between 30 and 2000;    -   q4 represents the number of repeat units in P4 and has a value        between 1 and 50;    -   q5 represents the number of repeat units in P5 and has a value        between 30 and 2000;    -   r represents the number of polymeric arms covalently attached to        the Core;    -   s represents the number of hydroxyl-containing arms covalently        attached to the Core; and    -   t represents the number of hydrophobic-containing copolymeric        arms covalently attached to the Core; and        wherein:    -   i) the molar ratio of r to s is in the range of between 40:1 and        1:40; and    -   ii) when t is at least 1:        -   a) the molar ratio of r to t is in the range of between 40:1            and 1:40;        -   b) the molar ratio oft to s is in the range of between 40:1            and 1:40; or        -   c) combinations thereof.

In certain embodiments, the one or more star macromolecules representedby Formula (I) may comprise a two-arm type of star macromolecule, suchas when t is not present (i.e., t=0). In another aspect of theinvention, the one or more star macromolecules represented by Formula(I) may comprise a three-arm type of star macromolecule, such as when tis present (i.e., t=1 or greater).

In certain embodiments, the hydroxyl-containing copolymeric segment P4of Formula (I) may be represented by P4a, wherein P4a may compriserepeat units of monomeric residues of polymerized monomers, wherein atleast one of the monomeric residues or a plurality of the monomericresidues is a hydroxyl-containing monomeric residue, and at least one ofthe monomeric residues or a plurality of the monomeric residues is ahydrophobic monomeric residue. In certain embodiments, for example, P4amay be represented by the designation of ((P6)_(q6)-(P7)_(q7)) or((P6)_(q6)-co-(P7)_(q7)), wherein P6 represents a hydroxyl-containingsegment (homopolymeric or copolymeric) comprising repeat units ofmonomeric residues of polymerized hydroxyl-containing monomers; P7represents a hydrophobic polymeric segment comprised of repeat units ofmonomeric residues of polymerized hydrophobic monomers; q6 representsthe number of repeat units in P6 and has a value between 1 and 50; q7represents the number of repeat units in P7 and has a value between 1and 50; and the sum of q6+q7 equals no more than 50 (i.e., no more thanq4), and wherein the term “co” represents that the hydroxyl-containingmonomeric residues of P6 are co-polymerized (such as blockcopolymerization or random copolymerization) with the hydrophobicmonomeric residues of P7.

In certain embodiments, the hydroxyl-containing copolymeric segment P4of Formula (I) may be represented by P4b, wherein P4b may compriserepeat units of monomeric residues of polymerized monomers, wherein atleast one of the monomeric residues or a plurality of the monomericresidues is a hydroxyl-containing monomeric residue, and at least one ofthe monomeric residues or a plurality of the monomeric residues is ahydrophilic monomeric residue. In certain embodiments, for example, P4bmay be represented by the designation of ((P6)_(q6)-(P8)_(q8)) or((P6)_(q6)-co-(P8)_(q8)), wherein P6 represents a hydroxyl-containingsegment (homopolymeric or copolymeric) comprising repeat units ofmonomeric residues of polymerized hydroxyl-containing monomers; P8represents a hydrophobic polymeric segment comprised of repeat units ofmonomeric residues of polymerized hydrophobic monomers; q6 representsthe number of repeat units in P6 and has a value between 1 and 50; q8represents the number of repeat units in P8 and has a value between 1and 50; and the sum of q6+q8 equals no more than 50 (i.e., no more thanq4), and wherein the term “co” represents that the hydroxyl-containingmonomeric residues of P6 are co-polymerized with the hydrophobicmonomeric residues of P8.

Suitable hydrophobic monomers for P1, for the at least one hydrophobicmonomers of P4 and P4a, or P7, that may be used to form an arm orsegment of an arm, such as a polymeric segment of an arm, of a starmacromolecule may include, but is not limited to styrene, methylacrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, t-butylacrylate, 2-ethylhexyl acrylate, decyl acrylate, octyl acrylate; methylmethacrylate; ethyl methacrylate; n-butyl methacrylate; iso-butylmethacrylate; t-butyl methacrylate; 2-ethylhexyl methacrylate; decylmethacrylate; methyl ethacrylate; ethyl ethacrylate; n-butylethacrylate; iso-butyl ethacrylate; t-butyl ethacrylate; 2-ethylhexylethacrylate; decyl ethacrylate; 2,3-dihydroxypropyl acrylate;2,3-dihydroxypropyl methacrylate; 2-hydroxypropyl acrylate;hydroxypropyl methacrylate; glycidyl methacrylate; glycidyl acrylate,acrylamides, styrene; styrene optionally substituted with one or moreC1-C12 straight or branched chain alkyl groups; or alkylacrylate. Forexample hydrophobic monomers may comprise methacrylate monomersfunctionalized with thymine, adenine, cytosine, or guanine, or acrylatemonomers functionalized with thymine, adenine, cytosine, or guanine, orstyrene monomers functionalized with thymine, adenine, cytosine, orguanine, or vinyl monomers functionalized with thymine, adenine,cytosine, or guanine, or acrylamide monomer functionalized with thymine,adenine, cytosine, or guanine. For example, the hydrophobic monomer maycomprise styrene; alpha-methylstyrene; t-butylstyrene; p-methylstyrene;methyl methacrylate; or t-butyl-acrylate. For example, the hydrophobicmonomer may comprise styrene. In certain embodiments, the hydrophobicmonomer may comprise a protected functional group.

In certain embodiments, the star macromolecules as defined by Formula(I) comprise a hydrophobic polymeric segment represented by P1, which iscomprised predominantly of repeat units of monomeric residues ofpolymerized hydrophobic monomers, for example, P1 may be comprisedsubstantially, mostly, or entirely of repeat units of monomeric residuesof polymerized hydrophobic monomers. In certain embodiments, thehydrophobic polymeric segment represented by P1 may be a hydrophobiccopolymeric segment comprised of one or more different polymerizedhydrophobic monomeric residues, such as two or three differenthydrophobic monomeric residues copolymerized (in either block or randomcopolymerization form).

Suitable star macromolecules, according to Formula (I), may include starmacromolecules wherein, P4a represents a block or randomhydroxyl-containing copolymeric segment comprised of repeat units ofmonomeric residues of polymerized monomers, wherein at least one of themonomeric residues or a plurality of the monomeric residues is ahydroxyl-containing monomeric residue, and at least one of the monomericresidues or a plurality of the monomeric residues is a hydrophobicmonomeric residue; wherein q4a may have a value of between 1 to 100, forexample, between 1 to 60, such as, between 1 to 45; between 5 to 40;between 8 to 35; between 10 to 30; between 12 to 25; between 14 to 20;between 15 to 30; or between 5 to 20; and wherein the molar ratio of rto s may be in the range of between 40:1 to 1:40, for example between40:1 to 2:1, such as between 8:1 to 3:1, and when t is at least 1: themolar ratio of r to t may be in the range of between 40:1 to 1:40, forexample between 40:1 to 2:1, such as between 8:1 to 3:1 the molar ratiooft to s may be in the range of between 40:1 to 1:40, for examplebetween 40:1 to 2:1, such as between 8:1 to 3:1, or combinationsthereof.

In certain embodiments, for example, P4a may be represented by thedesignation of ((P6)_(q6)-(P7)_(q7)) or ((P6)_(q6)-co-(P7)_(q7)),wherein P6 represents a hydroxyl-containing segment (homopolymeric orcopolymeric) comprising repeat units of monomeric residues ofpolymerized hydroxyl-containing monomers; P7 represents a hydrophobicpolymeric segment comprised of repeat units of monomeric residues ofpolymerized hydrophobic monomers; q6 represents the number of repeatunits in P6 and has a value between 1 and 50; q7 represents the numberof repeat units in P7 and has a value between 1 and 50; and the sum ofq6+q7 equals no more than 50 (i.e., no more than q4), and wherein theterm “co” represents that the hydroxyl-containing monomeric residues ofP6 are co-polymerized (such as block copolymerization or randomcopolymerization) with the hydrophobic monomeric residues of P7.

Suitable hydrophilic monomers for P2, P3, for the at least onehydrophilic monomers of P4 and P4b, P5, or P8, that may be used to forman arm or segment of an arm, such as a polymeric segment of an arm, of astar macromolecule may include, but is not limited to,2-Acrylamido-2-methylpropane sulfonic acid (AMPS), styrene sulphonicacid, protected and unprotected acrylic acids and methacrylic acidsincluding; ethacrylic acid, methyl acrylate, ethyl acrylate, d-butylacrylate, iso-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate,decyl acrylate, octyl acrylate; methyl methacrylate; ethyl methacrylate;n-butyl methacrylate; iso-butyl methacrylate; t-butyl methacrylate;2-ethylhexyl methacrylate; decyl methacrylate; methyl ethacrylate; ethylethacrylate; n-butyl ethacrylate; iso-butyl ethacrylate; t-butylethacrylate; 2-ethylhexyl ethacrylate; decyl ethacrylate;2,3-dihydroxypropyl acrylate; 2,3-dihydroxypropyl methacrylate;2-hydroxyethyl acrylate; 2-hydroxypropyl acrylate; hydroxypropylmethacrylate; glyceryl monoacrylate; glyceryl monoethacrylate; glycidylmethacrylate; glycidyl acrylate; acrylamide; methacrylamide;ethacrylamide; N-methyl acrylamide; N,N-dimethyl acrylamide;N,N-dimethyl methacrylamide; N-ethyl acrylamide; N-isopropyl acrylamide;N-butyl acrylamide; N-t-butyl acrylamide; N,N-di-n-butyl acrylamide;N,N-diethylacryl amide; N-octyl acrylamide; N-octadecyl acrylamide;N,N-diethylacryl amide; N-phenyl acrylamide; N-methyl methacrylamide;N-ethyl methacrylamide; N-dodecyl methacrylamide; N,N-dimethylaminoethylacrylamide; quaternised N,N-dimethylaminoethyl acrylamide;N,N-dimethylaminoethyl methacrylamide; quaternisedN,N-dimethylaminoethyl methacrylamide; N,N-dimethylaminoethyl acrylate;N,N-dimethylaminoethyl methacrylate; quaternised N,N-dimethyl-aminoethylacrylate; quaternised N,N-dimethylaminoethyl methacrylate,2-hydroxyethyl acrylate; 2-hydroxyethyl methacrylate; 2-hydroxyethylethacrylate; glyceryl acrylate; 2-methoxyethyl acrylate; 2-methoxyethylmethacrylate; 2-methoxyethyl ethacrylate; 2-ethoxyethyl acrylate;2-ethoxyethyl methacrylate; 2-ethoxyethyl ethacrylate; maleic acid;maleic anhydride and its half esters; fumaric acid; itaconic acid;itaconic anhydride and its half esters; crotonic acid; angelic acid;diallyldimethyl ammonium chloride; vinyl pyrrolidone vinyl imidazole;methyl vinyl ether; methyl vinyl ketone; maleimide; vinyl pyridine;vinyl pyridine-N-oxide; vinyl furan; styrene sulphonic acid and itssalts; allyl alcohol; allyl citrate; allyl tartrate; vinyl acetate;vinyl alcohol; vinyl caprolactam; vinyl acetamide; or vinyl formamide.For example, the hydrophilic monomer may comprise protected andunprotected acrylic acid, such as methacrylic acid, ethacrylic acid,methyl acrylate, ethyl acrylate, á-butyl acrylate, iso-butyl acrylate,t-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octyl acrylate;methyl acrylate; methyl methacrylate; methyl ethacrylate; ethylacrylate; ethyl methacrylate; ethyl ethacrylate; n-butyl acrylate;n-butyl methacrylate; n-butyl ethacrylate; 2-ethyl hexyl acrylate;2-ethylhexyl methacrylate; 2-ethylhexyl ethacrylate; N-octyl acrylamide;2-methoxyethyl acrylate; 2-hydroxyethyl acrylate; N,N-dimethylaminoethylacrylate; N,N-dimethylaminoethyl methacrylate; acrylic acid; methacrylicacid; N-t-butylacrylamide; N-sec-butylacrylamide;N,N-dimethylacrylamide; N,N-dibutylacrylamide;N,N-dihydroxyethyllacrylamide; 2-hydroxyethyl acrylate; 2-hydroxyethylmethacrylate; benzyl acrylate; 4-butoxycarbonylphenyl acrylate; butylacrylate; 4-cyanobutyl acrylate; cyclohexyl acrylate; dodecyl acrylate;2-ethylhexyl acrylate; heptyl acrylate; iso-butyl acrylate;3-methoxybutyl acrylate; 3-methoxypropyl acrylate; methyl acrylate;N-butyl acryl amide; N,N-dibutyl acrylamide; ethyl acrylate;methoxyethyl acrylate; hydroxyethyl acrylate; or diethyleneglycolethylacrylate. For example, the hydrophilic monomer may comprise protectedand unprotected acrylic acid, such as methacrylic acid, ethacrylic acid,methyl acrylate, ethyl acrylate, α-butyl acrylate, iso-butyl acrylate,t-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octyl acrylate;2-hydroxyethyl acrylate; N-isopropylacrylamide; ethylene glycolmethacrylate; (polyethylene glycol) methacrylate; or quaternizeddimethylaminoethyl methacrylate. For example, the hydrophilic monomermay comprise acrylic acid, methacrylic acid, 2-hydroxyethyl acrylate,acrylamide, vinyl pyrrolidone, vinyl pyridine, styrene sulphonic acid,PEG-methacrylate, 2-(dimethylamino)ethyl methacrylate,2-(trimethylamino)ethyl methacrylate, 2-acrylamido-2-methylpropanesulphonic acid, Acrylic acid, Acrylic anhydride, Beta-CarboxyethylAcrylate, Methacrylic acid, 4-Methacryloxyethyl trimellitic anhydride,3-Methacryloyl-(l)-lysine, o-Nitrobenzyl methacrylate,2-Propene-1-sulfonic acid, 2-Sulfoethyl methacrylate, Trichloroacrylicacid, 4-Vinylbenzoic acid, acrylamide/s, 2-(N,N-Dimethylamino)-ethylacrylate, N-[2-N,N-Dimethylamino)-ethyl]methacrylamide,2-(N,N-Dimethylamino)-ethyl methacrylate,3-Dimethylaminoneopentylacrylate,N-[3-(N,N-methylamino)-propyl]acrylamide,N-[3-(N,N-Dimethylamino)-propyl] methacrylamide, 2-N-Morpholinoethylacrylate, 2-N-Morpholinoethyl methacrylate, 3-Methacryloyl-(l)-lysine,N,N-Diallylamine, Diallyldimethyl, 2-Aminoethyl methacrylamide,N-(2-aminoethyl) methacrylamide hydrochloride,N-(3-Aminopropyl)-methacrylamide hydrochloride,N-(t-BOC-aminopropyl)-acrylamide, 2-(t-Butylamino)ethyl methacrylate,2-(N,N-Diethylamino)-ethyl methacrylate (DEAEMA),2-Diisopropylaminoethyl methacrylate. For example, the hydrophilicmonomer may comprise acrylic acid.

Suitable star macromolecules, according to Formula (I), may include starmacromolecules wherein, P4b represents a block or randomhydroxyl-containing copolymeric segment comprised of repeat units ofmonomeric residues of polymerized monomers, wherein at least one of themonomeric residues or a plurality of the monomeric residues is ahydroxyl-containing monomeric residue, and at least one of the monomericresidues or a plurality of the monomeric residues is a hydrophilicmonomeric residue; wherein q4b may have a value of between 1 to 100, forexample, between 1 to 60, such as, between 1 to 45; between 5 to 40;between 8 to 35; between 10 to 30; between 12 to 25; between 14 to 20;between 15 to 30; or between 5 to 20; and wherein the molar ratio of rto s may be in the range of between 40:1 to 1:40, for example between40:1 to 2:1, such as between 8:1 to 3:1, and when t is at least 1: themolar ratio of r to t may be in the range of between 40:1 to 1:40, forexample between 40:1 to 2:1, such as between 8:1 to 3:1, the molar ratiooft to s may be in the range of between 40:1 to 1:40, for examplebetween 40:1 to 2:1, such as between 8:1 to 3:1, or combinationsthereof.

In certain embodiments, for example, P4b may be represented by thedesignation of ((P6)_(q6)-(P8)_(q8)) or ((P6)_(q6)-co-(P8)_(q8)),wherein P6 represents a hydroxyl-containing segment (homopolymeric orcopolymeric) comprising repeat units of monomeric residues ofpolymerized hydroxyl-containing monomers; P8 represents a hydrophobicpolymeric segment comprised of repeat units of monomeric residues ofpolymerized hydrophobic monomers; q6 represents the number of repeatunits in P6 and has a value between 1 and 50; q8 represents the numberof repeat units in P8 and has a value between 1 and 50; and the sum ofq6+q8 equals no more than 50 (i.e., no more than q4), and wherein theterm “co” represents that the hydroxyl-containing monomeric residues ofP6 are co-polymerized with the hydrophobic monomeric residues of P8.

Suitable hydroxyl-containing monomers for P4, P4a, P4b, or P6 that maybe used to form a hydroxyl-containing segment may include, but are notlimited to, HEA (hydroxyethyl acrylate), HEMA (hydroxyethylmethacrylate), poly ethoxy ethyl methacrylate,1-(acryloyloxy)-3-(methacryloyloxy)-2-propanol, 1,1,1-trimethylolpropanediallyl ether, 1,1,1-trimethylolpropane monoallyl ether, 1,3-glyceryldimethacrylate, 2-hydroxy-3-chloropropyl methacrylate, 2-hydroxyethylacrylate, 2-hydroxyethyl methacrylate, low acid grade, 2-hydroxypropylacrylate, 4-(2-acryloxyethoxy)-2-hydroxybenzophenone, 4-hydroxybutylacrylate, 4-methacryloxy-2-hydroxybenzophenone, 4-tert-butoxystyrene,beta-carboxyethyl acrylate, bisphenol a-bis(2-hydroxypropyl) acrylate,glycerol monomethacrylate, hydroxypolyethoxy allyl ether, hydroxypropylmethacrylate, N-(2-hydroxypropyl)methacrylamide, n-hydroxyethylacrylamide, poly(ethylene glycol) (2000) monomethacrylate,poly(propylene glycol) (300) monomethacrylate, sorbitol acrylate,sorbitol methacrylate, pentaerythritol mono-acrylate, pentaerythritolmono-methacrylate, N-[tris(hydroxymethyl) methyl] acrylamide,trimethylolpropane monoallyl ether, sodium 1-allyloxy-2 hydroxypropylsulfonate, guar, cellulose, carbohydrates, proteins, peptides, sialicacids, glycosylates, glycopolymers, vinyl alcohol, poly(vinyl alcohol),keratin, carrageenan, guar like substances.

Suitable monomers that may be used to form a core of a starmacromolecule may include, but are not limited to, a multifunctionalmonomer, for example, a hexafunctional monomer, a pentafunctionalmonomer, a tetrafunctional monomer, a trifunctional monomer, or adifunctional monomer. For example, a crosslinker may be a hydrophobicmonomer or a hydrophilic monomer, such as a hydrophobic multifunctionalmonomer or a hydrophilic multifunctional monomer, for example, ahydrophobic difunctional monomer or a hydrophilic difunctional monomer.For example, the crosslinker may be a hydrophobic crosslinker,including, but not limited to, 1,2-divinylbenzene; 1,3-divinylbenzene;1,4-divinylbenzene; 1,2-ethanediol di(meth)acrylate; 1,3-propanedioldi(meth)acrylate; 1,4butanediol di(meth)acrylate, 1,5-hexanedioldi(meth)acrylate; divinylbenzene; ethyleneglycol di(meth)acrylate;di(ethylene glycol) diacrylate (DEGlyDA); propyleneglycoldi(meth)acrylate; butyleneglycol di(meth)acrylate; triethyleneglycoldi(meth)acrylate; polyethyleneglycol di(meth)acrylate;polypropyleneglycol di(meth)acrylate; polybutyleneglycoldi(meth)acrylate; allyl(meth)acrylate; glycerol di(meth)acrylate;trimethylolpropane tri(meth)acrylate; pentaerythritoltetra(meth)acrylate; allyl methacrylate; or allyl acrylate. For example,the crosslinker may be di(ethylene glycol) diacrylate (DEGlyDA) ordivinylbenzene. For example, the crosslinker may be divinylbenzene.

Suitable thickening crosslinkers (or thickening crosslinking agent) mayinclude, but are not limited to boric acid, borates, boronic acids,sodium borate, mineralized borate, mineralized boric acid, borax,time-released boric acid additives, boric acid derivatives, borate-typeadditives, such as borates, aluminum (including aluminates), zirconium(including zirconates), and titanium (including titanates), chromium(including chromates), antimony (including antimonates) containingcompounds. These suitable thickening crosslinkers (sometimes referred toas thickening boric acid crosslinkers or thickening boron-typecrosslinkers), work by chemically linking together (crosslinking) linearpolymers, such as star macromolecules comprising hydroxyl-containingpolymeric arms) in a hydraulic fracturing fluid creating highermolecular weight polymer compounds. Selection of the particularthickening crosslinking agent may be based upon the type of gellingagent being used in the hydraulic fracturing fluid. For example, thethickening crosslinking agent may include crosslinking with boron ions,such as from an aqueous borax/boric acid solution (such as to prepare aborate-crosslinked hydraulic fracturing fluid). For example, thethickening crosslinking agent, such as an aluminium phosphate, aluminiumester, or aluminium phosphate-ester, may be employed to form acrosslinked gel system. In addition, the pH of the water in thehydraulic fracturing fluid may be in the range of about 7-11, such as8-10, to permit effective crosslinking to occur.

In certain embodiments, the star macromolecule composition of thepresent invention, when dissolved in water at a concentration of 0.6 wt.% form a homogeneous gel, and have an increase in dynamic viscosity ofat least 5,000 cP in a 0.2 wt. % Borax aqueous solution, according tothe Borate-Crosslinker Thickening Test, relative to the dynamicviscosity of the homogeneous gel with 0.0 wt % Borax aqueous solution(i.e., in the absence of Borax crosslinker thickening agent). Forexample, in certain embodiments, the star macromolecule composition ofthe present invention, when dissolved in water at a concentration of 0.6wt. % form a homogeneous gel, and have an increase in dynamic viscosityof at least 6,000 cP in a 0.2 wt. % Borax aqueous solution, according tothe Borate-Crosslinker Thickening Test, relative to the dynamicviscosity of the homogeneous gel with 0.0 wt. % Borax aqueous solution(i.e., in the absence of Borax crosslinker thickening agent), such as anincrease in dynamic viscosity of at least 7,000 cP in a 0.2 wt. % Boraxaqueous solution; at least 8,000 cP; at least 9,000 cP; at least 10,000cP; at least 12,000 cP; at least 15,000 cP; at least 17,000 cP; at least20,000 cP; at least 22,000 cP; at least 23,000 cP; or an increase indynamic viscosity of at least 25,000 cP in a 0.2 wt. % Borax aqueoussolution, according to the Borate-Crosslinker Thickening Test, relativeto the dynamic viscosity of the homogeneous gel with 0.0 wt. % Boraxaqueous solution. For example, in certain embodiments, the starmacromolecule composition of the present invention, when dissolved inwater at a concentration of 0.6 wt. % form a homogeneous gel, and havean increase in dynamic viscosity in the range of between 5,000 cP to30,000 cP in a 0.2 wt. % Borax aqueous solution, according to theBorate-Crosslinker Thickening Test, relative to the dynamic viscosity ofthe homogeneous gel with 0.0 wt. % Borax aqueous solution (i.e., in theabsence of Borax crosslinker thickening agent), such as an increase indynamic viscosity in the range of between 5,000 cP to 28,000 cP in a 0.2wt. % Borax aqueous solution; in the range of between 5,000 cP to 26,000cP; between 5,000 cP to 25,000 cP; between 5,000 cP to 20,000 cP;between 5,000 cP to 15,000 cP; between 5,000 cP to 14,000 cP; between5,000 cP to 12,000 cP; between 5,000 cP to 10,000 cP; between 5,000 cPto 8,000 cP; between 7,000 cP to 30,000 cP; between 7,000 cP to 25,000cP; between 7,000 cP to 20,000 cP; between 7,000 cP to 15,000 cP;between 10,000 cP to 15,000 cP; between 10,000 cP to 20,000 cP; between10,000 cP to 25,000 cP; between 15,000 cP to 30,000 cP; between 20,000cP to 25,000 cP; or an increase in dynamic viscosity between 25,000 cPto 30,000 cP in a 0.2 wt. % Borax aqueous solution, according to theBorate-Crosslinker Thickening Test, relative to the dynamic viscosity ofthe homogeneous gel with 0.0 wt. % Borax aqueous solution.

In certain embodiments, the star macromolecule composition of thepresent invention, when dissolved in water at a concentration of 0.6 wt.% form a homogeneous gel, and have a positive % increase in dynamicviscosity of at least 10% in a 0.2 wt. % Borax aqueous solution,according to the Borate-Crosslinker Thickening Test, relative to thedynamic viscosity of the homogeneous gel with 0.0 wt. % Borax aqueoussolution (i.e., in the absence of Borax crosslinker thickening agent).For example, in certain embodiments, the star macromolecule compositionof the present invention, when dissolved in water at a concentration of0.6 wt. % form a homogeneous gel, and have a positive % increase indynamic viscosity of at least 12% in a 0.2 wt. % Borax aqueous solution,according to the Borate-Crosslinker Thickening Test, relative to thedynamic viscosity of the homogeneous gel with 0.0 wt. % Borax aqueoussolution (i.e., in the absence of Borax crosslinker thickening agent),such as a positive % increase in dynamic viscosity of at least 13% in a0.2 wt. % Borax aqueous solution; at least 14%; at least 15%; at least16%; at least 17%; at least 18%; at least 20%; at least 22%; at least23%; at least 24%; or a positive % increase in dynamic viscosity of atleast 25% in a 0.2 wt. % Borax aqueous solution, according to theBorate-Crosslinker Thickening Test, relative to the dynamic viscosity ofthe homogeneous gel with 0.0 wt. % Borax aqueous solution. For example,in certain embodiments, the star macromolecule composition of thepresent invention, when dissolved in water at a concentration of 0.6 wt.% form a homogeneous gel, and have a positive % increase in dynamicviscosity in the range of between 10% to 30% in a 0.2 wt. % Boraxaqueous solution, according to the Borate-Crosslinker Thickening Test,relative to the dynamic viscosity of the homogeneous gel with 0.0 wt. %Borax aqueous solution (i.e., in the absence of Borax crosslinkerthickening agent), such as an increase in dynamic viscosity in the rangeof between 10% to 25% in a 0.2 wt. % Borax aqueous solution; in therange of between 10% to 20%; between 10% to 15%; between 10% to 13%;between 15% to 30%; between 15% to 25%; between 15% to 20%; between 20%to 30%; between 20% to 25%; or an increase in dynamic viscosity between25% to 30% in a 0.2 wt. % Borax aqueous solution, according to theBorate-Crosslinker Thickening Test, relative to the dynamic viscosity ofthe homogeneous gel with 0.0 wt. % Borax aqueous solution.

Suitable star macromolecules may include, but are not limited to, amikto star macromolecule, a water-soluble star macromolecule, agel-forming star macromolecule, thickening agent star macromolecules,hydraulic fracturing fluid thickening star macromolecules, hydraulicfracturing fluid gelling star macromolecules, or combinations thereof.In certain embodiments, the star macromolecule may have a molecularweight of greater than 100,000 g/mol, for example, between 100,000 g/moland 5,000,000 g/mol, such as between 100,000 g/mol and 4,000,000 g/mol;between 100,000 g/mol and 3,000,000 g/mol; between 100,000 g/mol and2,000,000 g/mol; between 125,000 g/mol and 1,750,000 g/mol; between150,000 g/mol and 1,750,000 g/mol; between 200,000 g/mol and 1,500,000g/mol; between 225,000 g/mol and 1,250,000 g/mol; between 125,000 g/moland 1,000,000 g/mol; between 125,000 g/mol and 900,000 g/mol; between125,000 g/mol and 800,000 g/mol; between 125,000 g/mol and 700,000g/mol; between 150,000 g/mol and 650,000 g/mol; between 200,000 g/moland 600,000 g/mol; between 225,000 g/mol and 650,000 g/mol; between250,000 g/mol and 550,000 g/mol; between 350,000 g/mol and 500,000g/mol; between 300,000 g/mol and 500,000 g/mol; or between 350,000 g/moland 750,000 g/mol.

Suitable star macromolecules may have a polydispersity index (PDI) of8.0 or less, for example, a PDI of 7.0 or less, such as 6.0 or less; 5.0or less; 4.0 or less; 3.0 or less; 2.5 or less; 2.0 or less; or a PDI of1.7 or less. For example, a star macromolecule may have a PDT of between1.0 to 8.0, such as between 1.0 and 8.0; between 1.0 and 7.0; between1.0 and 6.0; between 1.0 and 5.0; between 1.0 and 4.0; between 1.0 and3.0; between 1.0 and 2.5; between 2.0 and 8.0; between 2.0 and 5.0;between 2.5 and 7.0; between 3.0 and 7.5; between 3.5 and 6.0; between1.0 and 2.3; between 1.0 and 2.0; between 1.0 and 1.9; between 1.0 and1.8; between 1.0 and 1.7; between 1.0 and 1.6; between 1.0 and 1.5;between 1.0 and 1.4; between 1.0 and 1.3; between 1.0 and 1.2; between1.0 and 1.1; between 1.05 and 1.75; between 1.1 and 1.7; between 1.15and 1.65; or between 1.15 and 1.55.

Suitable star macromolecules may comprise arms that are of the same typeor a different type and are homopolymeric, copolymeric (sometimesdesignated by “-co-”), comprise multiple block segment, random segments,gradient segments and or no particular segments. In certain embodiments,the star macromolecule may comprise, for example, one or more arm-types,such as, two or more, three or more, four or more, or five or morearm-types. Suitable arm types may include, but are not limited to,homopolymeric arms, copolymeric arms, such as random copolymeric arms orblock copolymeric arms, or combinations thereof. For example, a starmacromolecule may comprise homopolymeric arms and copolymeric arms, suchas block copolymeric arms. Suitable arm types may also include, but arenot limited to, hydrophilic arms, hydrophobic arms, or amphiphilic arms.In certain embodiments, a star macromolecule arm may comprisehydrophilic polymeric segments comprising hydrophilic monomericresidues, hydroxyl-containing polymeric segments comprisinghydroxyl-containing monomeric residues, hydrophobic polymeric segmentscomprising hydrophobic monomeric residues, amphiphilic polymericsegments comprising amphiphilic monomeric residues, or combinationsthereof. For example, in certain embodiments, a star macromolecule maycomprise homopolymeric arms and copolymeric arms, such as hydrophilichomopolymeric arms, copolymeric arms comprising hydrophilic polymericsegments and hydroxyl-containing polymeric segments, and copolymericarms comprising hydrophilic polymeric segments and hydrophobic polymericsegments. In certain embodiments, a star macromolecule may comprisepolymeric arms comprising predominantly hydrophilic polymeric segments,and one or more different copolymeric arms, such as two or moredifferent copolymeric arms, comprising a first copolymeric armcomprising a hydrophilic polymeric segment and a predominantlyhydroxyl-containing polymeric segment, and a second copolymeric armcomprising a hydrophilic polymeric segment and a predominantlyhydrophobic polymeric segment.

Suitable star macromolecules may also comprise arms that are covalentlylinked to the core of the star macromolecule. In certain embodiments,the arms of a star macromolecule may be covalently linked to the core ofthe star macromolecule via crosslinking, such as crosslinking with acrosslinker, for example, a hydrophobic difunctional crosslinker or ahydrophilic difunctional crosslinker. For example, arms of a starmacromolecule, such as homopolymeric arms and block copolymeric arms ofa mikto star macromolecule, may be covalently linked together to form acore by crosslinking an end of the arms with a crosslinker, such as witha hydrophobic difunctional crosslinker or a hydrophilic difunctionalcrosslinker. For example, arms of a star macromolecule, such ashydrophilic polymeric arms and copolymeric arms (block or random, orcontaining both block and random copolymeric segments) of a mikto starmacromolecule, may be covalently linked together to form a core bycrosslinking an end of the arms with a crosslinker, such as with ahydrophobic difunctional crosslinker or a hydrophilic difunctionalcrosslinker.

Suitable star macromolecules may also comprise arms of varying lengthand/or degree of polymerization. In certain embodiments, for example, astar macromolecule may comprise homopolymeric arms and block copolymericarms, wherein the homopolymeric arms of a shorter length and/or a lesserdegree of polymerization in relation to the block copolymeric arms. Incertain embodiments, for example, a star macromolecule may comprise ahydrophilic polymeric arms and one or more different copolymeric arms,wherein the hydrophilic polymeric arms are of a shorter length and/or alesser degree of polymerization in relation to the one or more differentcopolymeric arms. In certain embodiments, for example, a starmacromolecule may comprise homopolymeric arms and block copolymericarms, wherein the block copolymeric arms of a longer length and/or agreater degree of polymerization in relation to the homopolymeric arms.In certain embodiments, a star macromolecule may comprise hydrophilichomopolymeric arms and block copolymeric arms, comprising (i)hydrophobic polymeric segments distal to the star core and hydrophilicpolymeric segments that are proximal to the core of the star, wherein adistal portion of the hydrophilic polymeric segments of the copolymericarm extends beyond a distal portion of the hydrophilic homopolymericarms, and (ii) hydroxyl-containing polymeric segments distal to the starcore and hydrophilic polymeric segments that are proximal to the core ofthe star, wherein a distal portion of the hydrophilic polymeric segmentsof the copolymeric arm extends beyond a distal portion of thehydrophilic homopolymeric arms. For example, a star macromolecule maycomprise hydrophilic homopolymeric arms comprising polymerizedhydrophilic monomeric residues and block copolymeric arms comprising (i)hydrophobic polymeric segments distal to the core of the star andhydrophilic polymeric segments that are proximal to the core of thestar, wherein the distal hydrophobic polymeric segments extend beyondthe most distal portion, in relation to the core, of the hydrophilichomopolymeric arms, and/or wherein a distal portion of the proximalhydrophilic polymeric segments of the copolymeric arm extend beyond themost distal portion, in relation to the core, of the hydrophilichomopolymeric arms, (ii) hydroxyl-containing polymeric segments distalto the core of the star and hydrophilic polymeric segments that areproximal to the core of the star, wherein the distal hydroxyl-containingpolymeric segments extend beyond the most distal portion, in relation tothe core, of the hydrophilic homopolymeric arms, and/or wherein a distalportion of the proximal hydrophilic polymeric segments of thecopolymeric arm extend beyond the most distal portion, in relation tothe core, of the hydrophilic homopolymeric arms. In certain embodiments,a star macromolecule may comprise hydrophilic homopolymeric arms andblock copolymeric arms, comprising (i) hydrophobic polymeric segmentsdistal to the star core and hydrophilic polymeric segments that areproximal to the star core, wherein the degree of polymerization of thehydrophilic polymeric segments of the copolymeric arms are greater than,for example, 20% greater than, such as between 30% to 300% greater than,between 40% to 250%, between 50% to 200%, or between 75% to 250% greaterthan, the degree of polymerization of the hydrophilic homopolymericarms, such that a distal portion of the hydrophilic polymeric segmentsof the copolymeric arm extends beyond the a distal portion of thehydrophilic homopolymeric arms, and (ii) hydroxyl-containing polymericsegments distal to the star core and hydrophilic polymeric segments thatare proximal to the star core, wherein the degree of polymerization ofthe hydrophilic polymeric segments of the copolymeric arms are greaterthan, for example, 20% greater than, such as between 30% to 300% greaterthan, between 40% to 250%, between 50% to 200%, or between 75% to 250%greater than, the degree of polymerization of the hydrophilichomopolymeric arms, such that a distal portion of the hydrophilicpolymeric segments of the copolymeric arms extends beyond the a distalportion of the hydrophilic homopolymeric arms.

In certain embodiments, a star macromolecule may comprise hydrophilichomopolymeric arms comprising polymerized hydrophilic monomeric residuesand block copolymeric arms comprising (i) hydrophobic polymeric segmentsdistal to the core of the star and hydrophilic polymeric segmentsproximal to the core of the star, (ii) hydroxyl-containing polymericsegments distal to the core of the star and hydrophilic polymericsegments proximal to the core of the star, wherein the polymerizedhydrophilic monomeric residues of the homopolymeric arm and thehydrophilic polymeric segments of the copolymeric arms may be derivedfrom the same hydrophilic monomers, and may have the same or differentdegree of polymerization, for example, a degree of polymerization ofbetween 50 to 500 monomeric residues, such as, between 50 to 400monomeric residues; between 50 to 300 monomeric residues; between 50 to200 monomeric residues; between 100 to 250 monomeric residues; between125 to 175 monomeric residues; or between 150 to 300 monomeric residues.For example, a star macromolecule may comprise hydrophilic homopolymericarms comprising polymerized hydrophilic monomeric residues and blockcopolymeric arms comprising (i) hydrophobic polymeric segments distal tothe core of the star and hydrophilic polymeric segments proximal to thecore of the star, (ii) hydroxyl-containing polymeric segments distal tothe core of the star and hydrophilic polymeric segments proximal to thecore of the star, wherein the polymerized hydrophilic monomeric residuesof the homopolymeric arm and the hydrophilic polymeric segments of thecopolymeric arms may be derived from the same hydrophilic monomers, andmay have the same degree of polymerization, and wherein the hydrophobicpolymeric segments of the copolymeric arms may have a degree ofpolymerization of between 1 to 60 monomeric residues, such as between 1to 50 monomeric residues; between 1 to 45 monomeric residues; between 5to 40 monomeric residues; between 8 to 35 monomeric residues; between 10to 30 monomeric residues; between 12 to 25 monomeric residues; between14 to 20 monomeric residues; between 15 to 30 monomeric residues; orbetween 5 to 20 monomeric residues.

Suitable star macromolecules may have a wide range of total number ofarms, for example, a star macromolecule may comprise greater than 3arms. For example, a suitable star macromolecule may comprise between 3and 1000 arms, such as between 3 and 800 arms; between 3 and 500 arms;between 5 and 650 arms; between 5 and 500 arms; between 50 and 250 arms;between 100 and 900 arms; between 250 and 750 arms; between 500 and 1000arms; between 15 and 100 arms; between 15 and 90 arms; between 15 and 80arms; between 15 and 70 arms; between 15 and 60 arms; between 15 and 50arms; between 20 and 50 arms; between 25 and 45 arms; between 25 and 35arms; between 30 and 45 arms; or between 30 and 50 arms.

Suitable star macromolecules may have more than one arm type, such astwo or more different arm types, or three or more different arm types,where in a molar ratio of the different arm types may be between 40:1and 1:40, such as between 40:1 and 1:1; between 30:1 and 1:1; between20:1 and 1:1; between 15:1 and 1:1; between 10:1 and 1:1; between 5:1 to3:1; between 8:1 to 1:8; between 7:1 to 1:10; between 5:1 to 1:20;between 10:1 to 1:30; between 1:1 to 1:25; between 20:1 to 1:20; orbetween 3:1 to 1:8. For example, a star macromolecule comprising twodifferent arm types, such as a homopolymeric arm, for example, ahydrophilic homopolymeric arm, and a copolymeric arm, for example, acopolymeric arm comprising hydrophilic polymeric segments andhydrophobic polymeric segments, may have a molar ratio of the twodifferent arm types between 40:1 to 1:40, such as between 40:1 to 2:1;between 30:1 to 2:1; between 20:1 to 2:1; between 15:1 to 2:1; between10:1 to 2:1; between 9:1 to 2:1; between 8:1 to 2:1; between 7:1 to 2:1;between 6:1 to 2:1; between 5:1 to 2:1; between 4:1 to 2:1; between 3:1to 2:1; between 2:1 to 1:1; between 8:1 to 3:1; between 7:1 to 2:1;between 5:1 to 3:1; between 8:1 to 1:8; between 7:1 to 1:10; between 5:1to 1:20; between 10:1 to 1:30; between 1:1 to 1:25; between 20:1 to1:20; or between 3:1 to 1:8, and a copolymeric arm comprisinghydrophilic polymeric segments and hydroxyl-containing polymericsegments, may have a molar ratio of the two different arm types between40:1 to 1:40, such as between 40:1 to 2:1; between 30:1 to 2:1; between20:1 to 2:1; between 15:1 to 2:1; between 10:1 to 2:1; between 9:1 to2:1; between 8:1 to 2:1; between 7:1 to 2:1; between 6:1 to 2:1; between5:1 to 2:1; between 4:1 to 2:1; between 3:1 to 2:1; between 2:1 to 1:1;between 8:1 to 3:1; between 7:1 to 2:1; between 5:1 to 3:1; between 8:1to 1:8; between 7:1 to 1:10; between 5:1 to 1:20; between 10:1 to 1:30;between 1:1 to 1:25; between 20:1 to 1:20; or between 3:1 to 1:8.

Suitable star macromolecules may include, but is not limited to,comprising arms having a molecular weight of greater than 10,000 g/mol.For example, a star macromolecule may comprise arms having a molecularweight of between 10,000 g/mol and 500,000 g/mol, such as between 10,000g/mol and 400,000 g/mol; between 10,000 g/mol and 300,000 g/mol; between10,000 g/mol and 200,000 g/mol; between 10,000 g/mol and 175,000 g/mol;between 10,000 g/mol and 150,000 g/mol; between 10,000 g/mol and 125,000g/mol; between 10,000 g/mol and 100,000 g/mol; between 10,000 g/mol and90,000 g/mol; between 10,000 g/mol and 80,000 g/mol; between 10,000g/mol and 70,000 g/mol; between 60,000 g/mol and 50,000 g/mol; between10,000 g/mol and 40,000 g/mol; between 10,000 g/mol and 30,000 g/mol;between 10,000 g/mol and 20,000 g/mol; between 20,000 g/mol and 175,000g/mol; between 20,000 g/mol and 100,000 g/mol; between 20,000 g/mol and75,000 g/mol; between 20,000 g/mol and 50,000 g/mol; between 15,000g/mol and 45,000 g/mol; between 50,000 g/mol and 350,000 g/mol; between100,000 g/mol and 250,000 g/mol; between 75,000 g/mol and 300,000 g/mol;or between 15,000 g/mol and 30,000 g/mol.

Suitable arms of a star macromolecule may include, but is not limitedto, arms having an HLB value of at least 17 (wherein the HLB iscalculated per the formula set forth in the test procedures). Forexample, suitable arms of a star macromolecule may have an HLB value ofgreater than 17.25, such as greater than 18.5; at least 19; between 17.5to 20; between 17.5 to 19.5; between 18 to 20; between 18.5 to 20;between 19 to 20; between 19.5 to 20; between 18 to 19.5; between 18.5to 19.75; between 18.2 to 19.2; or between 18.75 to 19.5.

Suitable hydrophobic polymeric segments of a copolymeric arm of a starmacromolecule may include, but is not limited to, hydrophobic polymericsegments having an HLB value of less than 8. For example, suitablehydrophobic polymeric segments may have an HLB value of less than 7,such as less than 6; less than 5; less than 4; less than 3; less than 2;or about 1.

Suitable arms of a star macromolecule may include, but is not limitedto, arms having a polydispersity index (PDI) value of less than 4.0. Forexample, suitable arms of a star macromolecule may have PDI value ofless than 3.5, such as less than 3.0; less than 2.75; less than 2.5;less than 2.25; less than 2.0; or less than 1.7. For example, suitablearms of a star macromolecule may have PDI value of between 1.0 to 4.0,such as 1.0 to 3.5; between 1.0 to 3.0; between 1.0 to 2.5; between 1.0and 2.3; between 1.0 and 2.0; between 1.0 and 1.9; between 1.0 and 1.8;between 1.0 and 1.7; between 1.0 and 1.6; between 1.0 and 1.5; between1.0 and 1.4; between 1.0 and 1.3; between 1.0 and 1.2; between 1.0 and1.1; between 1.05 and 1.75; between 1.1 and 1.7; between 1.4 and 1.8;between 1.3 and 1.6; between 1.6 and 2.0; between 1.15 and 1.65; orbetween 1.15 and 1.55.

Suitable cores of a star macromolecule may be formed by or derived from,but is not limited to, crosslinking of a plurality of arms and acrosslinker. For example, a core may be formed by or derived fromcrosslinking of a plurality of homopolymeric arms and a plurality ofcopolymeric arms with a crosslinker, such as a multifunctional monomercrosslinker, for example, a hydrophobic difunctional monomercrosslinker. In certain embodiments, the core may be formed or derivedfrom crosslinking a plurality of hydrophilic homopolymeric arms and afirst plurality of copolymeric arms, comprising block hydrophilicpolymeric segments and block hydrophobic polymeric segments, and asecond plurality of copolymeric arms, comprising block hydrophilicpolymeric segments and block hydroxyl-containing polymeric segments,with a crosslinker, such as a hydrophobic difunctional monomercrosslinker, for example divinylbenzene, wherein the molar ratio of thehomopolymeric arms to the first copolymeric arms may be between 40:1 to1:40, such as between 40:1 to 2:1; between 30:1 to 2:1; between 20:1 to2:1, between 15:1 to 2:1; between 10:1 to 2:1; between 9:1 to 2:1;between 8:1 to 2:1; between 7:1 to 2:1; between 6:1 to 2:1; between 5:1to 2:1; between 4:1 to 2:1; between 3:1 to 2:1; between 2:1 to 1:1;between 8:1 to 3:1; between 7:1 to 2:1; between 5:1 to 3:1; between 8:1to 1:8; between 7:1 to 1:10; between 5:1 to 1:20; between 10:1 to 1:30;between 1:1 to 1:25; between 20:1 to 1:20; or between 3:1 to 1:8, andthe molar ratio of the homopolymeric arms to the second copolymeric armsmay be between 40:1 to 1:40, such as between 40:1 to 2:1; between 30:1to 2:1; between 20:1 to 2:1, between 15:1 to 2:1; between 10:1 to 2:1;between 9:1 to 2:1; between 8:1 to 2:1; between 7:1 to 2:1; between 6:1to 2:1; between 5:1 to 2:1; between 4:1 to 2:1; between 3:1 to 2:1;between 2:1 to 1:1; between 8:1 to 3:1; between 7:1 to 2:1; between 5:1to 3:1; between 8:1 to 1:8; between 7:1 to 1:10; between 5:1 to 1:20;between 10:1 to 1:30; between 1:1 to 1:25; between 20:1 to 1:20; orbetween 3:1 to 1:8.

Suitable star macromolecules may include, but is not limited to,comprising a core having a molecular weight of greater than 3,000 g/mol.For example, a star macromolecule may comprise a core having a molecularweight of between 3,000 g/mol and 90,000 g/mol, such as between 3,000g/mol and 45,000 g/mol; between 3,000 g/mol and 40,000 g/mol; between3,000 g/mol and 30,000 g/mol; between 3,000 g/mol and 20,000 g/mol;between 3,000 g/mol and 15,000 g/mol; between 5,000 g/mol and 40,000g/mol; between 6,000 g/mol and 30,000 g/mol; between 7,000 g/mol and25,000 g/mol; between 8,000 g/mol and 20,000 g/mol; between 5,000 g/moland 15,000 g/mol; between 7,000 g/mol and 12,000 g/mol; between 5,000g/mol and 9,000 g/mol; between 8,000 g/mol and 10,000 g/mol; or between9,000 g/mol and 15,000 g/mol.

Suitable star macromolecules may be used to form a clear, homogeneousgel when dissolved in water at a concentration of at least 0.05 wt. % ata pH of about 7.5 at STP. For example, a star macromolecule may form aclear, homogeneous gel when dissolved in water at a concentration ofbetween 0.05 wt % to 3 wt %, such as between 0.1 wt. % to 2.5 wt. %;between 0.1 wt. % to 2 wt. %; between 0.2 wt. % to 2.0 wt. %; between0.2 wt. % to 1.5 wt. %; between 0.2 wt. % to 1.0 wt. %; between 0.2 wt.% to 2.5 wt. %; between 0.3 wt. % to 2.5 wt. %; between 0.4 wt. % to 2.0wt. %; between 0.5 wt. % to 2.0 wt. %; between 0.6 wt. % to 2.0 wt. %;between 0.7 wt. % to 1.5 wt. %; between 0.8 wt. % to 1.2 wt. %; between0.9 wt. % to 1.1 wt. %; between 0.5 wt. % to 2.5 wt. %; between 0.75 wt.% to 1.5 wt. %; or between 0.8 wt. % to 1.6 wt. %.

Suitable star macromolecules, in accordance with the pH Efficiency RangeTest Procedure described below herein, may be used to form a clear,homogeneous gel, wherein the star macromolecule at a concentration of0.4 wt. %, may have a viscosity of at least 20,000 cP, at a pH ofbetween about 4 to about 12, for example, at a pH of between about 5 toabout 11.5 such as at a pH of between about 5 to about 11; between about5 to about 10.5; between about 5 to about 10; between about 5 to about9.5; between about 5 to about 9; between about 5 to about 8.5; betweenabout 5 to about 8; between about 6 to about 11; between about 5.5 toabout 10; between about 6 to about 9; between about 6.5 to about 8.5;between about 7 to about 8; between about 7.5 to about 8.5; or betweenabout 6.5 to about 7.5.

In certain embodiments, for example, suitable star macromolecules, inaccordance with the pH Efficiency Range Test Procedure described belowherein, may be used to form a clear, homogeneous gel, wherein the starmacromolecule at a concentration of 0.4 wt. %, may have a viscosity ofat least 20,000 cP at a pH between about 5.5 to about 11. For example,at a pH between about 5.5 to about 11 may have a viscosity of at least30,000 cP, such as, at least 40,000 cP; between 20,000 cP to 250,000 cP;between 20,000 cP to 250,000 cP; between 20,000 cP to 225,000 cP;between 20,000 cP to 200,000 cP; between 20,000 cP to 175,000 cP;between 20,000 cP to 150,000 cP; between 20,000 cP to 125,000 cP;between 30,000 cP to 250,000 cP; between 30,000 cP to 200,000 cP;between 40,000 cP to 175,000 cP; or between 40,000 cP to 150,000 cP. Forexample, a gel at a pH between about 6 to about 11 may have a viscosityof at least 20,000 cP, such as, at least 30,000 cP; at least 40,000 cP;between 20,000 cP to 250,000 cP; between 20,000 cP to 250,000 cP;between 20,000 cP to 225,000 cP; between 20,000 cP to 200,000 cP;between 20,000 cP to 175,000 cP; between 20,000 cP to 150,000 cP;between 20,000 cP to 125,000 cP; between 30,000 cP to 250,000 cP;between 30,000 cP to 200,000 cP; between 40,000 cP to 175,000 cP; orbetween 40,000 cP to 150,000 cP. For example, at a pH between about 7 toabout 10.5 may have a viscosity of at least 60,000 cP, such as at least70,000 cP; between 60,000 cP to 250,000 cP; between 60,000 cP to 225,000cP; between 60,000 cP to 200,000 cP; between 60,000 cP to 175,000 cP;between 60,000 cP to 150,000 cP; between 60,000 cP to 125,000 cP;between 60,000 cP to 115,000 cP; between 60,000 cP to 105,000 cP; orbetween 60,000 cP to 100,000 cP. For example, at a pH between about 4.5to about 9.0 may have a viscosity of at least 95,000 cP, such as atleast 100,000 cP; between 95,000 cP to 250,000 cP; between 95,000 cP to225,000 cP; between 95,000 cP to 200,000 cP; between 95,000 cP to175,000 cP; between 95,000 cP to 150,000 cP; between 95,000 cP to125,000 cP; between 95,000 cP to 115,000 cP; or between 95,000 cP to105,000 cP.

Suitable star macromolecules, in accordance with the Dynamic Viscosity &Shear-Thinning Test Procedure described below herein, may be used toform a clear, homogeneous gel, wherein the star macromolecule at aconcentration of 0.4 wt. %, may have a viscosity of less than 5,000 cPat a shear rate of 4 sec⁻, such as a viscosity of less than 4,000 cP.For example, the star macromolecule at a concentration of 0.4 wt. %, mayhave a viscosity have a viscosity of less than 5,000 cP at a shear rateof 6 sec⁻¹, such as a viscosity of less than 4,000 cP or less than 3,000cP. For example, a gel may have a viscosity of less than 15,000 cP at ashear rate of 0.7 sec⁻¹, such as a viscosity of less than 14,000 cP orless than 13,000 cP. Suitable gels may include, but is not limited to,gels having shear-thinning value of at least 5, such as a shear-thinningvalue of at least 6, or between 5 to 15, such as between 5 to 15;between 7 to 12; between 8 to 10; or between 6 to 13.

Suitable star macromolecules, in accordance with the Dynamic Viscosity &Shear-Thinning Test Procedure described below herein, include those thathave a shear-thinning value of at least 6, such as a shear-thinningvalue of between 6 to 100, such as between 15 to 90; between 20 to 80;between 25 to 70; between 25 to 50; or between 30 to 40.

Suitable star macromolecules, in accordance with the Salt-Induced BreakTest Procedure described below herein, include those that have asalt-induced break value of at least 50%, such as a salt-induced breakvalue of between 65% to 100%, such as between 75% to 100%; between 80%to 95%; between 75% to 90%; between 50% to 85%; between 70% to 95%; orbetween 60% to 100%.

Suitable star macromolecules, in accordance with the pH Efficiency RangeTest Procedure described below herein, include those that have apH-induced break value of at least 15%, such as a pH-induced break valueof between 15% to 100%, such as between 25% to 100%; between 30% to 95%;between 40% to 90%; between 50% to 85%; between 70% to 95%; between 80%to 97%; between 90% to 99%; between 95% to 100%; or between 60% to 100%.

Suitable star macromolecules, in accordance with the Dynamic Viscosity &Shear-Thinning Test Procedure described below herein, include those thathave a dynamic viscosity value, of greater than 20,000 cP at 1 rpm, andat a concentration of 0.2 wt. %, such as a dynamic viscosity value ofgreater than 24,000 cP; greater than 28,000 cP; or greater than 30,000cP at a concentration of 0.2 wt. %.

Suitable emulsions may include, but is not limited to, emulsions thatare emulsifier-free and wherein the emulsion is thickened by a starmacromolecule. For example, the star macromolecule that may be includedin the emulsifier-free emulsion may be a water-soluble starmacromolecule, wherein the water-soluble star macromolecule emulsifiesthe emulsifier-free emulsion.

Suitable star macromolecules, include star macromolecules that have anemulsion value of greater than 60 minutes, for example, greater than 3hours, such as greater than 6 hours; greater than 10 hours; greater than20 hours; greater than 40 hours; or greater than 100 hours.

The term “star macromolecule composition” is understood to mean acomposition comprising at least one star macromolecule as defined byFormula (I), of the total star macromolecules in the composition, forexample, comprising predominantly star macromolecules as defined byFormula (I); such as comprising substantially star macromolecules asdefined by Formula (I); comprising mostly star macromolecules as definedby Formula (I). For example, the star macromolecule composition maycomprise in the range of between 0.001 wt. % to 100 wt. % of the starmacromolecule as defined by Formula (I), of the total starmacromolecules in the composition, such as in the range of between 0.01wt % to 10 wt. %; between 0.1 wt. % to 5 wt. %; between 0.01 wt. % to 3wt. %; between 0.001 wt. % to 1 wt. %; between 0.01 wt. % to 1.5 wt. %;or between 0.1 wt. % to 4.0 wt. %; of the total star macromolecules inthe composition. For example, the star macromolecule composition maycomprise predominantly star macromolecules having a molecular weightwithin 5%, for example, within 4%, 3%, 2% or 1%, of the molecular weightof the pre-determined star macromolecule represented by Formula (I),relative to the total star macromolecules in the composition, whereinthe PDI of the star macromolecules is in the range of between 1.0-8.0,for example, the star macromolecule as defined by Formula (I) has a PDIin the range of between 1.0 and 7.0; such as between 1.0 and 6.0;between 1.0 and 5.0; between 1.0 and 4.0; between 1.0 and 3.0; between1.0 and 2.0; between 2.0 and 8.0; between 3.0 and 7.0; between 2.0 and5.0; between 3.0 and 6.0; between 3.5 and 7.5; between 1.5 and 2.0; orbetween 1.5 and 2.5; and wherein each arm of the star macromoleculeindependently has a PDI in the range of between 1.0-4.0, for example,each arm of the star macromolecule, as defined by Formula (I),independently has a PDI in the range of between 1.0 and 3.5; such asbetween 1.0 and 3.0; between 1.0 and 2.5; between 1.0 and 2.0; between2.0 and 3.5; between 1.0 and 1.75; between 1.0 and 1.5; between 1.5 and2.0; or between 1.5 and 2.5. In certain embodiments, the starmacromolecule composition of the present invention comprises at leastone star macromolecule as defined by Formula (I) that results from thepreparation of one or more star macromolecule processes as describedherein, such as by the one-pot process, the arm first process, ATRP,CRP, RAFT, TEMPO, Nitroxide, LRP, CRP, anionic polymerization, cationicpolymerization, or combinations thereof.

Suitable star macromolecules, according to Formula (I), may include starmacromolecules wherein, for example, P1 comprises hydrophobic monomers,P2 comprises hydrophilic monomers, P3 comprises hydrophilic monomers, P4comprises hydroxyl-containing monomers, and P5 comprises hydrophilicmonomers. For example, star macromolecules, according to Formula (I),may include star macromolecules wherein q1 and q4 may have a value ofbetween 1 to 100, for example, between 1 to 60, such as, between 1 to45; between 5 to 40; between 8 to 35; between 10 to 30; between 12 to25; between 14 to 20; between 15 to 30; or between 5 to 20; and q2, q3and/or q5 have a value of between 50 to 500, for example, between 50 to400, such as, between 50 to 300; between 50 to 200; between 100 to 250;between 125 to 175; or between 150 to 300. For example, starmacromolecules, according to Formula (I), may include starmacromolecules wherein r, s, or t, or the sum of r and t, or the sum ofs and t, may be greater than 3, such as between 3 and 1000 arms, such asbetween 3 and 800 arms; between 3 and 500 arms; between 5 and 650 arms;between 5 and 500 arms; between 50 and 250 arms; between 100 and 900arms; between 250 and 750 arms; between 500 and 1000 arms; between 15and 100; between 15 and 90; between 15 and 80; between 15 and 70;between 15 and 60; between 15 and 50; between 20 and 50; between 25 and45; between 25 and 35; between 30 and 45; or between 30 and 50. Forexample, star macromolecules, according to Formula (I), may include starmacromolecules wherein the molar ratio of r to s may be in the range ofbetween 40:1 to 1:40, and when t is at least 1: the molar ratio of r tot may be in the range of between 40:1 to 1:40, or the molar ratio oft tos may be in the range of between 40:1 to 1:40, or combinations thereof.For example, the molar ratio of r to s, is in the range of between 40:1to 1:40, such as between 40:1 to 2:1; between 30:1 to 2:1; between 20:1to 2:1; between 15:1 to 2:1; between 10:1 to 2:1; between 9:1 to 2:1;between 8:1 to 2:1; between 7:1 to 2:1; between 6:1 to 2:1; between 5:1to 2:1; between 4:1 to 2:1; between 3:1 to 2:1; between 2:1 to 1:1;between 8:1 to 3:1; between 7:1 to 2:1; between 5:1 to 3:1; between 8:1to 1:8; between 7:1 to 1:10; between 5:1 to 1:20; between 10:1 to 1:30;between 1:1 to 1:25; between 20:1 to 1:20; or between 3:1 to 1:8. Forexample, when t is at least 1, the molar ratio of r to t, is in therange of between 40:1 to 1:40, such as between 30:1 to 2:1; between 20:1to 2:1; between 15:1 to 2:1; between 10:1 to 2:1; between 9:1 to 2:1;between 8:1 to 2:1; between 7:1 to 2:1; between 6:1 to 2:1; between 5:1to 2:1; between 4:1 to 2:1; between 3:1 to 2:1; between 2:1 to 1:1;between 8:1 to 3:1; between 7:1 to 2:1; between 5:1 to 3:1; between 8:1to 1:8; between 7:1 to 1:10; between 5:1 to 1:20; between 10:1 to 1:30;between 1:1 to 1:25; between 20:1 to 1:20; or between 3:1 to 1:8. Forexample, when t is at least 1, the molar ratio oft to s, is in the rangeof between 40:1 to 1:40, such as between 30:1 to 2:1; between 20:1 to2:1; between 15:1 to 2:1; between 10:1 to 2:1; between 9:1 to 2:1;between 8:1 to 2:1; between 7:1 to 2:1; between 6:1 to 2:1; between 5:1to 2:1; between 4:1 to 2:1; between 3:1 to 2:1; between 2:1 to 1:1;between 8:1 to 3:1; between 7:1 to 2:1; between 5:1 to 3:1; between 8:1to 1:8; between 7:1 to 1:10; between 5:1 to 1:20; between 10:1 to 1:30;between 1:1 to 1:25; between 20:1 to 1:20; or between 3:1 to 1:8.

In certain embodiments, star macromolecules according to Formula (I) mayinclude star macromolecules wherein the core may be derived fromcrosslinker monomers, such as hydrophobic crosslinker monomers. Forexample, star macromolecules, according to Formula (I), may include starmacromolecules wherein the core may comprise crosslinker monomericresidues, such as hydrophobic crosslinker monomeric residues. In certainembodiments, star macromolecules according to Formula (I), may includestar macromolecules wherein the polymerized monomeric residues of P1, orP2, or both, of the [(P1)_(q1)-(P2)_(q2)]_(t) arm may be homopolymericor copolymeric, such as random copolymeric or block copolymeric, andwherein the polymerized monomeric residues of P4, or P5, or both, of the[(P4)_(q4)-(P5)_(q5)]_(s) arm may be homopolymeric or copolymeric, suchas random copolymeric or block copolymeric.

Suitable star macromolecules, may include, but is not limited to, starmacromolecules formed by crosslinking the arms with a crosslinker, suchas crosslinking homopolymeric arms and block copolymeric arms with ahydrophobic crosslinker. For example, the homopolymeric arms and thecopolymeric arms of a star macromolecule may be covalently attached tothe core via crosslinkage with a crosslinker. For example, a core of aprepared star macromolecule may be prepared by crosslinking an end of ahomopolymeric arm with an end of a copolymeric arm, such as an end of ahydrophilic homopolymeric arm with a hydrophilic end of a copolymericarm. For example, the core of a prepared star macromolecules may beformed by crosslinking an ATRP-functional terminal group end of ahomopolymeric arm with an ATRP-functional terminal group end of acopolymeric arm.

Suitable initiators that may be used to form the star macromoleculesdisclosed herein, may include, but is not limited to, nitroxideinitiators, such as stable nitroxide initiators, for example,2,2,6,6-Tetramethylpiperidine-1-oxyl, sometimes called TEMPO; transitionmetal complexes, such cobalt containing complexes; ATRP initiators,comprising halides, such as, bromide, chloride, or iodide, andtransition metal sources, such as, copper, iron, ruthenium transitionmetal sources; iodide with RCTP catalysts, such as germanium or tincatalysts; RAFT initiators, such as dithioesters, dithiocarbamates, orxanthates; ITP catalysts, comprising iodides; tellurium compounds (e.g.,TERP); stibine compounds (e.g., SBRP); or bismuth compounds (e.g.,BIRP). For example, in certain embodiments, an initiator may furthercomprise a monomeric residue, a polymeric segment comprising monomericresidues, or a small-molecule. For example, in certain embodiments, aninitiator may comprise an ATRP initiator, wherein the ATRP initiatorserves as a terminal functional group. For example, in certainembodiments, an initiator may comprise an ATRP-functional terminalgroup, comprising an ATRP initiator, such as halides and transitionmetal sources.

Although any conventional method can be used for the synthesis of themulti-arm star macromolecules of the invention, free radicalpolymerization is the preferred and living/controlled radicalpolymerization (CRP) is the most preferred process.

Star polymers are nano-scale materials with a globular shape and can beformed by the “arm first” procedure, can have a crosslinked core and canoptionally possess multiple segmented arms of similar composition. Starscan be designed as homo-arm stars or mikto-arm stars.

Synthesis of star polymers of the invention can be accomplished by“living” polymerization techniques via one of three strategies: 1)core-first” which is accomplished by growing arms from a multifunctionalinitiator; 2) “coupling-onto” involving attaching preformed arms onto amultifunctional core and the 3) arm-first” method which involvescross-linking preformed linear arm precursors using a divinyl compound.

While all above controlled polymerization procedures are suitable forpreparation of an embodiment of the disclosed self assembling starmacromolecules. Other embodiments are also exemplified, for example, thepreparation of the self assembling multi-arm stars with narrow MWD, incontrast to prior art using ATRP. The reason for the use of theControlled Radical Polymerization process (CRP) known as ATRP; disclosedin U.S. Pat. Nos. 5,763,546; 5,807,937; 5,789,487; 5,945,491; 6,111,022;6,121,371; 6,124,411: 6,162,882: and U.S. patent application Ser. Nos.09/034,187; 09/018,554; 09/359,359; 09/359,591; 09/369,157; 09/126,768and 09/534,827, and discussed in numerous publications listed elsewherewith Matyjaszewski as co-author, which are hereby incorporated into thisapplication, is that convenient procedures were described for thepreparation of polymers displaying control over the polymer molecularweight, molecular weight distribution, composition, architecture,functionality and the preparation of molecular composites and tetheredpolymeric structures comprising radically (co)polymerizable monomers,and the preparation of controllable macromolecular structures under mildreaction conditions.

An aspect of the present invention relates to the preparation and use ofmulti-arm star macromolecules by an “arm first” approach, discussed byGao, H.; Matyjaszewski, K. JACS; 2007, 129, 11828. The paper and citedreferences therein are hereby incorporated by reference to describe thefundamentals of the synthetic procedure. The supplemental informationavailable within the cited reference provides a procedure forcalculation of the number of arms in the formed star macromolecule.

It is expected that biphasic systems such as a mini-emulsion or an abinitio emulsion system would also be suitable for this procedure sincemini-emulsion systems have been shown to function as dispersed bulkreactors [Min, K.; Gao, H.; Matyjaszewski, K. Journal of the AmericanChemical Society 2005, 127, 3825-3830] with the added advantage ofminimizing core-core coupling reactions based on compartmentalizationconsiderations.

In one embodiment star macromolecules are prepared with composition andmolecular weight of each segment predetermined to perform as rheologymodifiers in aqueous based solutions. The first formed segmented linearpolymer chains are chain extended with a crosslinker forming acrosslinked core.

In another embodiment a one-pot industrially scalable process for thepreparation of star macromolecules is provided wherein the arms comprisesegments selected to induce self assembly and wherein the selfassemblable star macromolecules are suitable for use as rheology controlagents in waterborne and solvent-borne coatings, adhesives, andfracturing fluid compositions.

An embodiment of the present invention can be exemplified by thepreparation of a multi-arm star macromolecule wherein the number of armsin the star macromolecule is between 5 and 1000, such as between 5 and500, preferentially between 10 and 250, with segments selected to induceself assembly when the star macromolecule is dispersed in a liquidwherein the self assemblable star macromolecules are suitable for use asthickening agents or rheology modifiers in cosmetic and personal carecompositions at low concentrations of the solid in the thickenedsolution, preferably less than 5 wt %, and optimally less than 1 wt %.The dispersion medium can comprise aqueous based systems or oil basedsystems.

Similar structures can also be prepared using the macromonomer method ora combination of the macromonomer and macroinitiator method in acontrolled polymerization process, or even through free radicalcopolymerization conducted on macromonomers, as known to those skilledin the art. [Gao, H.; Matyjaszewski, K. Chem.—Eur. J. 2009, 15,6107-6111.]

Both the macromonomer and macroinitiator procedures allow incorporationof polymer segments prepared by procedures other than CRP [WO 98/01480]into the final star macromolecule. Polymer segments can comprisesegments that are bio-degradable of are formed from monomers preparedfrom biological sources.

As noted above the first formed ATRP macroinitiator can be prepared byconducting a sequential ATRP (co)polymerization of hydrophobic andhydrophilic monomers or precursors thereof or can be prepared by otherpolymerization procedures that provide a functional terminal atom orgroup that can be converted into an ATRP initiator with a bifunctionalmolecule wherein one functionality comprises a transferable atom orgroup and the other functionality an atom or group that can react withthe functionality first present on the (co)polymer prepared by anon-ATRP procedure. [WO 98/01480]

In aqueous solutions, the composition and molecular weight of the outershell of hydrophobes, or agents that participate in molecularrecognition, can be selected to induce self-assembly into aggregates andact as physical crosslinkers. Above a certain concentration,corresponding to the formation of a reversible three dimensionalnetwork, the solutions will behave as physical gels thereby modifyingthe rheology of the solution.

In one embodiment, the polymer compositions of the invention havesignificantly lower critical concentration for network (gel) formationcompared to networks formed with block copolymers, graft and stars witha low specific number of attached arms due to:

-   -   multi-arm structure (many transient junctions possible between        hydrophobic parts of the stars)    -   very high molecular weight of each star (5 thousand to 5 million        or higher) allows high swelling ratio of the molecules in        solution    -   molecular organization on larger scales (>1 μm)

Whereas the examples above and below describe the preparation and use ofblock copolymers as arms with a well defined transition from one segmentto the adjoining segment a segmented copolymer with a gradient incomposition can also be utilized. The presence of a gradient can becreated by addition of a second monomer prior to consumption of thefirst monomer and will affect the volume fraction of monomer unitspresent in the transition form one domain to another. This would affectthe shear responsiveness of the formed star macromolecule.

Star macromolecules with narrow polydispersity comprising arms withblock copolymer segments can be formed with as few as 5 arms byselecting appropriate concentration of reagents, crosslinker andreaction temperature.

Star macromolecules can be prepared in a mini-emulsion or reversemini-emulsion polymerization system. The first formed block copolymersare used as reactive surfactants for star synthesis by reaction with aselected crosslinker in mini-emulsion.

In an embodiment, a star macromolecule may be represented by Formula Y:

wherein:Core represents a crosslinked polymeric segment;P1 represents a hydrophobic homopolymeric segment comprised of repeatunits of monomeric residues of polymerized hydrophobic monomers;P2 represents a hydrophilic homopolymeric segment comprised of repeatunits of monomeric residues of polymerized hydrophilic monomers;P3 represents a hydrophilic homopolymeric segment comprised of repeatunits of monomeric residues of polymerized hydrophilic monomers;P4 represents a hydroxyl-containing segment (homopolymeric orcopolymeric) comprised of repeat units of monomeric residues, where atleast one of the monomeric residues or a plurality of the monomericresidues is a hydroxyl-containing monomeric residue, of polymerizedmonomers;P5 represents a hydrophilic homopolymeric segment comprised of repeatunits of monomeric residues of polymerized hydrophilic monomers;q1 represents the number of repeat units in P1 and has a value between 1and 50;q2 represents the number of repeat units in P2 and has a value between30 and 2000;q3 represents the number of repeat units in P3 and has a value between30 and 2000;q4 represents the number of repeat units in P4 and has a value between 1and 50;q5 represents the number of repeat units in P5 and has a value between30 and 2000;r represents the number of homopolymeric arms covalently attached to theCore;s represents the number of hydroxyl-containing arms covalently attachedto the Core; andt represents the number of copolymeric arms covalently attached to theCore; andwherein:i) the molar ratio of r to tis in the range of between 40:1 and 2:1;ii) the molar ratio of r to s is in the range of between 40:1 and 2:1;iii) the molar ratio oft to s is in the range of between 40:1 and 1:40;oriv) combinations thereof.

In an embodiment, one or more star macromolecules may be represented byFormula Y, wherein the one or more star macromolecules may have amolecular weight of between 150,000 g/mol and 5,000,000 g/mol. In anembodiment, one or more star macromolecules may be represented byFormula Y, wherein the sum total number of arms (r+t) is between 15 and45, or the sum total number of arms (s+t) is between 15 and 45, or bothsum total number of arms (r+t) and sum total number of arms (s+t) areeach between 15 and 45. In an embodiment, one or more starmacromolecules may be represented by Formula Y, wherein the molar ratioof r to t is in the range of between 8:1 and 3:1, or the molar ratio ofs to t is in the range of between 8:1 and 3:1, or both the molar ratioof r to t and the molar ratio of s to t are each in the range of between8:1 and 3:1. In an embodiment, one or more star macromolecules may berepresented by Formula Y, wherein i) both q2 and q3 have a value greaterthan 100, and q2 is greater than q3; or ii) both q5 and q3 have a valuegreater than 100, and q5 is greater than q3; or iii) both q2 and q3 havea value greater than 100, and q5 and q3 have a value greater than 100,and q2 and q5 are greater than q3. In an embodiment, one or more starmacromolecules may be represented by Formula Y, wherein the armsrepresented by [(P1)_(q1)-(P2)_(q2)] and [(P4)_(q4)-(P5)_(q5)] have anHLB value greater than 18. In an embodiment, one or more starmacromolecules may be represented by Formula Y, wherein the P1homopolymeric segment is a hydrophobic homopolymeric segment having anHLB value of less than 8. In an embodiment, one or more starmacromolecules may be represented by Formula Y, wherein the corecomprises a hydrophobic crosslinked polymeric segment. In an embodiment,one or more star macromolecules may be represented by Formula Y, whereinthe star macromolecule is a water soluble mikto star macromolecule. Inan embodiment, one or more star macromolecules may be represented byFormula Y, wherein the star macromolecule, when dissolved in water at aconcentration of at least 0.2 wt. %, forms a clear, homogeneous gelhaving a viscosity of at least 20,000 cP.

In an embodiment, a dual-mechanism thickening agent, comprising a starmacromolecule represented by Formula Y having a molecular weight ofbetween 150,000 g/mol and 5,000,000 g/mol that forms a homogeneous gelwhen dissolved in water at a concentration of at least 0.05 wt. %;wherein the gel has: i) a dynamic viscosity of at least 20,000 cP; ii) asalt-induced break value of at least 60%; iii) a shear-thinning value ofat least 10; and/or iv) an emulsion value of greater than 12 hours. Inan embodiment, the dual-mechanism thickening agent comprising a starmacromolecules represented by Formula Y, wherein the gel-forming starmacromolecule has a viscosity of greater than 40,000 cP at a pH between6 to 11. In an embodiment, the dual-mechanism thickening agentcomprising a star macromolecules represented by Formula Y, wherein thegel-forming star macromolecule has a viscosity of less than 5,000 cP ata shear rate of 4 sec⁻¹. In an embodiment, the dual-mechanism thickeningagent comprising a star macromolecules represented by Formula Y, whereinthe gel-forming star macromolecule has a PDI of less than 2.5. In anembodiment, the dual-mechanism thickening agent comprising a starmacromolecules represented by Formula Y, wherein the gel-forming starmacromolecule is a water-soluble mikto star macromolecule. In anembodiment, the dual-mechanism thickening agent comprising a starmacromolecules represented by Formula Y, wherein the gel-forming starmacromolecule has between 15 to 45 arms. In an embodiment, thedual-mechanism thickening agent comprising a star macromoleculesrepresented by Formula Y, wherein the arms of the gel-forming starmacromolecule comprise: i) hydrophilic homopolymeric arms; ii)copolymeric arms, comprising: a) hydrophilic polymeric segments andhydrophobic polymeric segments; and b) hydrophilic polymeric segmentsand hydroxyl-containing polymeric segments. In an embodiment, thedual-mechanism thickening agent comprising a star macromoleculesrepresented by Formula Y, wherein the arms of the gel-forming starmacromolecule have an HLB of between 18 and 20.

In an embodiment, a fracturing fluid composition may comprising at least0.05 wt. % of a dual-mechanism thickening agent to improve waterflooding during enhanced oil recovery, wherein the dual-mechanismthickening agent is a star macromolecule comprising: a) a molecularweight of greater than 100,000 g/mol; b) a core having a hydrophobiccrosslinked polymeric segment; and c) a plurality of arms comprising atleast three types of arms, wherein: i) a first-arm-type extends beyond asecond-arm-type, and said first-arm-type has a hydrophobic segment onits distal end; and ii) a third-arm-type extends beyond asecond-arm-type, and said third-arm-type has a hydroxyl-containingsegment on its distal end; wherein the rheology-modifying compositionhas a shear-thinning value of at least 6. In an embodiment, thefracturing fluid composition may further comprise one or more boric acidadditives or borate-type additives.

EXAMPLES

TABLE 1 Abbreviation Name Form Purity Commercial Source MeCNAcetonitrile liquid 99.8%  Sigma Aldrich AA acrylic acid (formed bydeprotection) NA NA NA Anisole liquid 99% Sigma Aldrich AIBN2,2′-Azobis(2-methylpropionitrile) solid 98% Sigma Aldrich V-702,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) solid 99% Wako BoraxAnhydrous solid 98% Sigma Aldrich DEBMM diethyl 2-bromo-2-methylmalonateliquid 98% Sigma Aldrich DMF Diethylformamide liquid 98% Sigma AldrichDVB Divinylbenzene liquid 80% Sigma Aldrich EBiB Ethylα-bromoisobutyrate liquid 98% Sigma Aldrich FA formic acid liquid 99%Sigma Aldrich GMA Glycerol monomethacrylate liquid 99% Monomer-Polymer &Dajac Labs HCl hydrochloric acid liquid 37% Sigma Aldrich MMA methylmethacrylate liquid 99% Sigma Aldrich NaCl Sodium chloride solid 99.7% Fisher Chemical NaOH sodium hydroxide solid 98% Sigma Aldrich St Styreneliquid 99% Sigma Aldrich tBA tert-butyl acrylate liquid 98% SigmaAldrich THF Tetrahydrofuran liquid 99.9%  Sigma Aldrich Sn(EH)₂ tin(II)2-ethylhexanoate liquid 95% Sigma Aldrich TPMAtris(2-pyridylmethyl)amine solid 95% ATRP Solutions Me6TRENtris[2-(dimethylamino)ethyl]amine liquid 95% ATRP Solutions

Synthesis of Star Copolymers (Example 1) Example 1: Synthesis of[((MMA)₁₅-co-(GMA)₂)-(AA)₃₀₇]/[(AA)₂₀] Star Macromolecule (r to s is3:1)

The “one-pot” procedure was used for the preparation of a poly(acrylicacid) based miktoarm star macromolecule similar to that described inU.S. patent application Ser. No. 61/760,210, filed on Feb. 4, 2013,which is incorporated herein by reference in its entirety. The miktoarmstar macromolecule with [((MMA)₁₅-co-(GMA)₂)-(AA)₃₀₇] and [(AA)₂₀] arms(molar ratio of arms: 1/3) was prepared as follows.

STEP 1: Synthesis of Poly(methyl methacrylate)-co-Poly(glycerolmonomethacrylate) Macroinitiator [referred to herein as((MMA)₁₅-co-(GMA)₂)]

To prepare the ((MMA)₁₅-co-(GMA)₂) macroinitiator, the following molarratio of reagents was used: MMA/GMA DEBMM/CuBr₂/TPMA/AscorbicAcid=30/3/1/0.00165/0.01650.0043 in anisole (33% v/v). A 100 ml roundbottom flask was charged with 20 ml of MMA, 3 g of GMA, 1.19 ml ofDEBMM, 6 ml of anisole, and 0.8 ml of a pre-mixed CuBr₂/Me₆TREN in DMFsolution. The flask was sealed with a rubber septum and the solution waspurged with nitrogen for 1.0 hour, then placed in a 60° C. oil bath. Tothe flask was added 1.01 ml of Ascorbic Acid in DMF solution (14 mg ofAscorbic Acid in 3 mL of DMF) at the addition rate of 1 mL/h, over aperiod of 1 hour. After the reaction was continued for an additional 1hour and 40 minutes, the flask was opened to air and the reaction wasstopped. The resulting polymer was purified by precipitation intomethanol/water (1:1 v/v), and determined to have a molecular weight of2073 g/mol (as measured by NMR) and a PDI of 1.50 (as measured by GPC).Yield was 5.46 g of purified polymer.

STEPS 2-4: Synthesis of [(MMA)₁₅-co-(GMA)₂)-(AA)₃₀₇]/[(AA)₂₀] starmacromolecules in “one pot” (i.e., steps 2-4 in one pot):

STEP 2: Synthesis of [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] arms: Toprepare the [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] arms, the followingmolar ratio of reagents was used: tBA/((MMA)₁₅-co-(GMA)₂) (from Example1, Step 1)/EBiB/CuBr₂/Me₆TREN/V-70=200/0.25/0.75/0.01/0.05/0.025. In a22 ml vial was dissolved 17.2 mg CuBr₂ in 5.9 ml DMF and 0.1 ml Me₆TRENto make a stock solution of CuBr₂/Me₆TREN in DMF. A 250 ml round bottomflask was charged with 1.66 g of the ((MMA)₁₅-co-(GMA)₂) (from Example1), 60 ml of tBA, 30 ml of anisole (33%, v/v) as the solvent, and 1.98ml of the CuBr₂/Me₆TREN in DMF stock solution. After stirring theresulting solution for 10 min to dissolve the macroinitiator, the flaskwas sealed with a rubber septum, and purged with nitrogen for 40minutes, then heated to 65° C. In a separate 22 ml vial, 19.7 mg of V-70was dissolved in 1 ml of acetone, and the resulting solution was purgedwith N₂. The solution of V-70 in acetone was then injected in 0.1 mlaliquots every 20 minutes into the heated reaction via 1 ml syringeunder N₂. Samples were periodically taken for analysis, and once theconversion of monomer reached 64%, to the reaction was injected 0.23 mlof EBiB. Subsequently, an additional 0.1 ml of V-70 in acetone wasinjected every 30 minutes. Upon monomer conversion reaching 84%, thereaction flask was opened to air.

STEP 3: Cross-linking of [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] arms:To crosslink the [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] arms toprepare the [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] starmacromolecules, the following molar ratio of reagents was used:{[((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀]}/DVB/CuBr₂/Me₆TREN/AIBN=1/25/0.012/0.12/0.07in anisole. In a 22 ml vial was dissolved 10.1 mg CuBr₂ in 6.49 ml DMFand 0.12 ml Me₆TREN to make a stock solution of CuBr₂/Me₆TREN in DMF. Tothe reaction flask was added 3.2 ml of the CuBr₂/Me₆TREN in DMF stocksolution, 6.72 ml DVB, and 80 ml anisole. The resulting polymer solutionwas purged with N₂ for 1 h, and then heated to 95° C. To the reactionwas added AIBN in acetone solution at an addition rate of 0.32 mL/h (theaddition rate was adjusted during the polymerization process in order tocontrol the kinetics and exothermic effects of the reaction). After 2.5h, 0.8 mL of the CuBr₂/Me₆TREN in DMF stock solution was injected intothe reaction. Samples were periodically taken for analysis, and once theconversion of DVB reached 64% (at t=16 hours), the heating was stoppedand the flask was opened to air. The molecular weight of[((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] star macromolecule wasdetermined by GPC. Mn=71663 g/mol, Mp=204145 g/mol, having a PDI=2.85.The GPC results were present in FIG. 2.

STEP 4: Deprotection of [((MMA)₁₅-co-(GMA)₂)-(tBA)₃₀₇]/[(tBA)₂₀] starmacromolecules: To the resulting reaction mixture of Example 3 was added20 ml of formic acid and 0.1 ml sulfuric acid. The reaction mixture washeated up to 75° C. After 6 hours, the liquid was decanted from thereaction, and the solid polymer retained in the reaction flask waswashed with acetonitrile and acetone 3 times. The washed solid polymerwas then recovered from the flask and dried in vacuum oven at 40° C. for1 day. Yield: 24 g of purified [((MMA)₁₅-co-(GMA)₂)-(AA)₃₀₇]/[(AA)₂₀]star macromolecule (wherein the molar ratio of r to s is 3:1; P3 is AA,q3 is 20; P5 is AA, q5 is 307; P4 is ((MMA)₁₅-co-(GMA)₂), and in thedesignation of ((P6)_(q6)-co-(P7)_(q7)), P6 is GMA, q6 is 2, P7 is MMA,and q7 is 15).

Properties of Star Copolymer (Examples 2-3) Example 2: Shear ThinningTest in Water-Shear Thinning Property of Star Macromolecule asThickening Agents

The thickening and rheological properties of the aqueous solutions ofstar macromolecules synthesized in Examples 1 (at a concentration of 0.6wt %, and at a pH of 7.5), prepared according to the sample preparationprocedure described below, were investigated. The viscosity vs. shearrate was measured using a Spindle #25 according to the Dynamic Viscosity& Shear-Thinning Test Procedure described below. The results arepresented in FIG. 3 and Table 2.

TABLE 2 Shear Rate [s⁻¹] Viscosity in DI-Water @25° C. [cP] 0.066 1660000.11 113300 0.22 63400 0.44 35300 1.1 16990 2.2 9890 4.4 5950 6.6 438011 3062 22 1930 * Viscosity was measured using Brookfield LVDV-E,Spindle #25

Example 3: Borate-Crosslinked Test—Crosslinking Ability of StarMacromolecules as Thickening Agents

A borate-crosslinked system of the star macromolecule of Example 1 wasprepared according to the Borate-Crosslinker Thickening Test Procedure,and the resulting viscosity was measured and the Borate-CrosslinkerThickening Test value was determined.

A comparative example using [(St)₁₅-(AA)₂₅₀]/[(AA)₁₃₇] starmacromolecule (wherein the molar ratio of r to t is 4:1, and s=0;wherein P1 is St, q1 is 15, P2 is AA, q2 is 250, P3 is AA, and q3 is137), that doesn't contain hydroxyl groups, was also evaluated. The[(St)₁₅-(AA)₂₅₀]/[(AA)₁₃₇] star macromolecule (at a concentration of 0.6w.t. %) was prepared as a gel according to the sample preparationprocedure described below, and was also prepared as a borate-crosslinkedgel according to the Borate-Crosslinker Thickening Test Procedure, andthe resulting viscosity was measured and the Borate-CrosslinkerThickening Test value was determined.

The above-described Borate-crosslinked tests were performed on thehomogenized gel. The results are presented in Table 3.

TABLE 3 Viscosity at 1 rpm [cP] Without With cross-linker Starmacromolecule cross-linker 0.1 wt. % 0.2 wt. % Example 1 63400 6960074900 [(St)₁₅ − (AA)₂₅₀]/[(AA)₁₃₇] 357100 283700 169400

Test Procedures:

Sample Preparation

Aqueous gels at various concentrations (e.g., 0.2 wt. %, 0.25 wt %, 0.4wt. % 0.6 wt. %, 0.7 wt. % and 1.0 wt. %) were prepared as follows: 400mL of deionized (DI) water was transferred to 600 mL beaker and stirredwith an IKA overhead stirrer mounted with a 3-blade marine impeller.Water was stirred at 600 rpm to generate vortex and certain amount ofthickening agent powder was slowly sprinkled. The aqueous solution washeated to 30° C. and solid NaOH was added. The stirring rate wasincreased to 800 rpm for 5-10 min and then adjusted to 1600 rpm forabout 15-20 min until the temperature reached 80-90° C. The gel was thenhomogenized with a Silverson homogenizer equipped with a Square Holeworkhead and an Axial Flow workhead. The homogenizer stirring speed wasgradually increased to 4800±200 rpm and mixed for 35 min until a thickhomogeneous gel was obtained. A pH of the resulting gel was analyzedwith pH meter and adjusted (with NaOH) to pH=7.5.

Dynamic Viscosity & Shear-Thinning Test Procedure

A portion of the sample preparation was introduced into a BrookfieldLVDV-E Digital Viscometer, using either a spindle #31 or spindle #25 formixing, at STP, over a wide range of rates (e.g, 0.3-100 rpm) and theshear rate and viscosity was recorded. Viscosity measurements were takenin the following sequence, stopping the instrument after eachmeasurement for 5 minutes, 0.3, 0.5, 1, 2, 5, 10, 20, 30, 50, and 100rpm. The dynamic viscosity was determined as the viscosity in centipoise(cP) at 0.3 rpm or at 1 rpm. A shear-thinning value was determined bydividing the dynamic viscosity value at 0.3 rpm by the dynamic viscosityvalue at 20 rpm.

Borate-Crosslinker Thickening Test Procedure:

The following procedure was applied to measure the viscosity of theaqueous gels in the presence of borate crosslinker thickening agent(Borax). A Borax containing gel was prepared by adding 18 mg or 36 mg ofBorax anhydrous (to eventually result in formation of a 0.1 wt. % boratecrosslinker, or 0.2 wt. % borate crosslinker mixture, respectively) to avial, along with a certain amount of 0.6 wt. % gel of the starmacromolecule (prepared as described in the Sample PreparationProcedure) such that the resulting mixture has a total weight of 18 g.The borax and star macromolecule gel containing mixture were stirred at50° C. for 2 hours, and after cooling to room temperature, the pH of theresulting gel was analyzed with pH meter and adjusted with HCl, asnecessary, to pH=7.5˜7.8.

The Borate-Crosslinker Thickening Test value for the testedborate-crosslinked star macromolecule was measured and recorded as theviscosity (in centipoise, cP) at a given wt. % gel (0.6 wt. % of a starmacromolecule gel) in a given wt. % Borax concentration (0.2 wt. % of aBorax concentration), in accordance to the Dynamic Viscosity TestProcedure (using a Brookfield LVDV-E, Spindle #25 at T=25° C.) (forexample a viscosity of 50,000 cP at 0.6 wt % gel in a 0.2 wt. % Boraxconcentration).

Salt-Induced Break Test Procedure

A portion of the sample preparation was introduced into 20 ml glassscintillation vial. A measured portion of NaCl was added into the vial(e.g., 0.05 wt. % relative to the total weight of the sample in thevial. After the NaCl addition was complete, the vial was closed andshaken for 10 min. Then, the viscosity of the sample was measured inaccordance with the Dynamic Viscosity & Shear-Thinning Test Procedure,above, and the dynamic viscosity at 1 rpm was recorded. This procedurewas repeated for differing concentrations of NaCl. The salt-inducedbreak value, in percent, is determined by the following equation:Initial Dynamic Viscosity(0% NaCl)−Dynamic Viscosity(0.05 wt. %NaCl)/Initial Dynamic Viscosity(0% NaCl)×100%.

pH Efficiency Range Test Procedure

An aqueous gel composition at 0.4 wt % was prepared for a starmacromolecule of the present invention, at a starting pH of around 5 anda separate aqueous gel composition at 0.2 wt. % aqueous gel compositionof Carbopol ETD 2020, at a starting pH of around 3, was prepared bymixing and heating, as necessary (e.g., vigorous mixing at a temperatureof about 60° C.). Then, the viscosity of the sample was measured inaccordance with the Dynamic Viscosity & Shear-Thinning Test Procedure,above, and the dynamic viscosity at 1 rpm was recorded. This procedurewas repeated for differing pH values, adjusted by addition of sodiumhydroxide. The pH-induced break value, in percent, is determined by thefollowing equation:Dynamic Viscosity(at 1 rpm) at pH7.5−Dynamic Viscosity(at 1 rpm) atpH5/Dynamic Viscosity(at 1 rpm) at pH7.5×100%.

Emulsion Test Procedure

340 mL of water was added to a 500 ml beaker and stirred vigorously withan overhead stirrer. 1.6 g of the material to be tested for emulsifyingeffect was added and heated to 80 C. The solution was pH adjusted with400 mg of NaOH and stirring continued until a homogeneous gel wasobtained. 60 ml sunflower oil was added while vigorous stirring wascontinued with an overhead stirrer at 80 C for 10 min or untilhomogenous emulsion is obtained. The mixture was allowed to cool to roomtemperature. Once the system cools to room temperature start timer. Theemulsion value is the time, in minutes, it takes for the system to formtwo visible layers (phase separation).

Strong Gel Test Procedure

10 ml portion of the sample preparation material was introduced into a20 ml glass scintillation vial. After the transfer was complete, thevial was placed on a surface and remained undisturbed for about 20minutes at STP. The vial was then gently inverted (turned-upside down)and placed on the surface and a timer started. If after 5 minutes, thereis no visible flow then the sample is said to be a strong gel.

Hydrophilic-Lipophilic (HLB) Arm/Segment CalculationHLB=20*Mh/Mwhere Mh is the molecular mass of the hydrophilic portion of thepolymeric arm or segment, and M is the molecular mass of the wholepolymeric arm or segment.

Hydrophilic-Lipophilic Macromolecule Calculation

${HLM} = {{\sum\limits_{n = 1}^{n = m}{M\; W_{n}{{xHLB}_{n}/20}\mspace{14mu}{divided}\mspace{14mu}{by}\mspace{14mu} 0.3\; M\; W_{core}}} + {\sum\limits_{n = 1}^{n = m}{M\; W_{n}}}}$where

-   -   MW_(n) is the molecular weight for the respective arm,    -   HLB_(n) is the HLB, as calculated from the HLB arm calculation,        for the respective arm, and    -   MW_(core) is the molecular weight for the core, and    -   M is the total number of arms.

What is claimed is:
 1. A dual-mechanism thickening agent, comprising astar macromolecule that forms a homogeneous gel when dissolved in waterat a concentration of at least 0.05 wt. %, wherein the gel exhibits: a)a dynamic viscosity of at least about 20,000 cP; b) a shear-thinningvalue of at least 10; c) an increase in dynamic viscosity of at leastabout 5,000 cP in a 0.2 wt. % Borax aqueous solution, according toBorate-Crosslinker Thickening Test; or d) combinations thereof; andwherein the star macromolecule comprises: i) a molecular weight ofbetween about 150,000 g/mol and about 5,000,000 g/mol; ii) a core and atleast three-types of arms; and iii) wherein at least one of thethree-types of arms comprises a hydrophilic polymeric or copolymericsegment proximal to the core and comprising repeat units of polymerizedhydrophilic monomeric residues; and a hydroxyl-containing polymeric orcopolymeric segment distal to the core comprising one or morepolymerized hydroxyl-containing residues.
 2. The dual-mechanismthickening agent of claim 1, wherein the star macromolecule has anincrease in dynamic viscosity in the range of between about 5,000 cP toabout 30,000 cP, or an increase in dynamic viscosity of at least about12%, in a 0.2 wt. % Borax aqueous solution, according to theBorate-Crosslinker Thickening Test, relative to the dynamic viscosity ofa homogeneous gel of the star macromolecule with 0.0 wt. % Borax aqueoussolution.
 3. The dual-mechanism thickening agent of claim 1, wherein thestar macromolecule has a viscosity of less than about 5,000 cP at ashear rate of 4 sec⁻¹.
 4. The dual-mechanism thickening agent of claim1, wherein the star macromolecule has a polydispersity index (“PDI”)between about 1.0 to about 8.0.
 5. The dual-mechanism thickening agentof claim 1, wherein the star macromolecule has a pH-induced break valueof at least about 50%.
 6. The dual-mechanism thickening agent of claim1, wherein the star macromolecule has an emulsion value of greater thanabout 12 hours.
 7. The dual-mechanism thickening agent of claim 1,wherein the star macromolecule is a water-soluble mikto starmacromolecule.
 8. The dual-mechanism thickening agent of claim 1,wherein the core comprises a hydrophobic crosslinked polymeric segment.9. The dual-mechanism thickening agent of claim 1, wherein the starmacromolecule is prepared by one or more star macromolecule processes,comprising: one-pot processes, arm first processes, Atom TransferRadical Polymerization (“ATRP”) processes, Controlled RadicalPolymerization (“CRP”) processes, Reversible Addition-FragmentationChain Transfer (“RAFT”) processes, 2,2,6,6-Tetramethylpiperidine-1-oxyl(“TEMPO”) processes, Nitroxide processes, Living Radical Polymerization(“LRP”) processes, anionic polymerization processes, cationicpolymerization processes, or combinations thereof.
 10. Thedual-mechanism thickening agent of claim 1, wherein the starmacromolecule is a gel-forming star macromolecule.
 11. A compositioncomprising the dual-mechanism thickening agent of claim
 1. 12. Thecomposition of claim 11, wherein the composition comprises at leastabout 0.05 wt. % of the star macromolecule.
 13. The composition of claim11, wherein the composition is a fracturing fluid thickening additive, adrilling well fluid thickening additive, a gelling agent, or an additiveto improve oil extraction from oil sands.
 14. The composition of claim11, wherein the composition is a rheology-modifying composition having ashear-thinning value of at least
 6. 15. The composition of claim 11,wherein the composition is a cosmetic composition, a personal carecomposition, a cleaning composition, an adhesive composition, a medicalor pharmaceutical composition, a paper application composition, anagricultural composition, a coating composition, a lubricantcomposition, an antifoaming composition, an antifreeze composition, acorrosion inhibitor composition, a detergent composition, an inkcomposition, or a combination thereof.
 16. The composition of claim 11,wherein the composition further comprises one or more boric acidadditives or borate-type additives.
 17. A fracturing fluid composition,comprising at least about 0.05 wt. % of a dual-mechanism thickeningagent to improve water flooding during enhanced oil recovery, whereinthe dual-mechanism thickening agent is a star macromolecule comprising:a) a molecular weight of greater than about 100,000 g/mol; b) a corehaving a hydrophobic crosslinked polymeric segment; and c) a pluralityof arms comprising at least three types of arms, wherein: i) afirst-arm-type extends beyond a second-arm-type, and said first-arm-typehas a hydrophobic segment on its distal end; and ii) a third-arm-typeextends beyond a second-arm-type, and said third-arm type has ahydroxyl-containing segment on its distal end and a hydrophilic segmentproximal to the core; wherein: A) the composition has a shear-thinningvalue of at least 6; and B) the star macromolecule, when dissolvedin: 1) water at a concentration of at least 0.05 wt. %, forms a clear,homogeneous gel, said gel having a dynamic viscosity of at least about20,000 cP; and 2) a 0.2 wt. % Borax aqueous solution, forms a gel, saidgel having an increase in dynamic viscosity of at least about 5,000 cP,or an increase in dynamic viscosity of at least 12%, according toBorate-Crosslinker Thickening Test, relative to the dynamic viscosity ofa homogeneous gel of the star macromolecule with 0.0 wt. % Borax aqueoussolution.
 18. The fracturing fluid composition of claim 17 furthercomprises one or more boric acid additives and borate-type additives.19. The fracturing fluid composition of claim 17 is a fracturing fluidthickening additive, a drilling well fluid thickening additive, agelling agent, or an additive to improve oil extraction from oil sands.20. The fracturing fluid composition of claim 17, wherein the starmacromolecule is prepared by one or more star macromolecule processes,comprising: one-pot processes, arm first processes, Atom TransferRadical Polymerization (“ATRP”) processes, Controlled RadicalPolymerization (“CRP”) processes, Reversible Addition-FragmentationChain Transfer (“RAFT”) processes, 2,2,6,6-Tetramethylpiperidine-1-oxyl(“TEMPO”) processes, Nitroxide processes, Living Radical Polymerization(“LRP”) processes, anionic polymerization processes, cationicpolymerization processes, or combinations thereof.